Artificial intelligence general catalog page link
1. Linux basic
Day01 notes
1.1 introduction to development
1. Three operating systems
1,Unix
Mac OS ,Solaris
2,Linux
RedHat,CentOS,Ubuntu 16.04(Teaching environment version)
3,Windows
win7,win8,win 10
2. VMware Workstation (testing, learning)
1,Powerful desktop virtual computer software
2,A powerful tool for developing, testing and deploying applications
3,teaching(Development, test and deployment)Environmental installation
1,download VMware Workstation Install package and install
2,download Linux Operating system image file.iso(Pure version) : Ubuntu 16.04
3,open VMware Workstation,file -> New virtual machine(Assemble the computer)
4,CD/DVD -> Insert disc(.iso file)
5,Turn on this virtual machine -> Power on
6,After installation, install a series of software and modules
2.1 Linux basic commands
3. Linux foundation
1,Terminal: used to input Linux command 1,Click on the picture 2,click "Search computer" -> gnome-terminal 2,Directory tree 1,root / : Represents the starting location of the file system 2,Path: represents a file/String for directory /home/tarena/AID09 3,Linux Basic format of command Command name [option] [parameter] #[] means the content is optional
4. Linux commands
1,pwd : Displays the current path
2,ls : Displays the details of the directory(Files, subdirectories)
1,Common options
ls -l : To list(Long format)Display file and directory details
ls -a : Show all(Include hidden) with . Start with hidden
ls -la
ls -al
3,route
1,Absolute path: with / Start path
2,Relative path: Not to / Start path
. current directory
.. Upper level directory
~ User home directory/Home directory(/home/tarena)
3,home directory/Home directory
1,Super user: root
2,When you create a user, you automatically/home Create a directory with the same name as the user name under,Home directory for this user
user name: tarena Home directory:/home/tarena
user name: zhanshen Home directory:/home/zhanshen
4,cd : Switch directory(route)
1,usage
cd route(Both absolute and relative paths are OK)
cd /home/tarena ,cd /home/tarena/aid1809
cd aid1809 #The premise is that the current home directory
2,cd Enter directly: return to the user's home directory/home/tarena
cd ~ : Return to user home directory
cd - : Switch back and forth from the two most recently accessed directories
3,TAB Key auto fill command/route(Skilled use!!!!!)
1,Fast speed
2,The path cannot be wrong,TAB If it doesn't come out, there is a problem with the path
4,practice
1,Switch to directory:/home/tarena/anaconda3/bin
cd /home/tarena/anaconda3/bin/
2,View the current path
pwd
3,List all contents of the current directory in list form(Include hidden)
ls -la
4,Switch to the directory above the current directory,Namely
: /home/tarena/anaconda3
cd ..
5,Switch to/etc catalogue,see/etc What's in the next section
cd /etc/
6,Switch directly to the user's home directory
cd
5,mkdir : Create 1 or n Directories(folder)
1,Format: mkdir Directory name 1 directory name 2 ...
2,Common options
-p : Create directory layer by layer
mkdir -p One/Two/Three/Go
# If the intermediate directory does not exist, create it directly
6,touch
1,effect
1,file does not exist -> establish
2,File exists -> Update file modification time with system time
2,Format: touch File name 1 file name 2 file name 3 ...
3,practice
1,Create directory under user home directory A1/B1/C1/D1
cd
mkdir -p A1/B1/C1/D1
2,stay D1 Create file under file1.txt file2.txt
cd A1/B1/C1/D1
touch file1.txt file2.txt
3,stay C1 Create file under file3.txt file4.txt
cd ..
touch file3.txt file4.txt
4,Switch to A1 catalogue,View the current path
cd ../../
pwd
5,Switch directly to the user's home directory
cd
7,Skill class
1,Automatic replenishment: TAB key
2,Turn up the history and execute the command: press the up and down keys on the keyboard
3,Clear screen: Ctrl + l perhaps clear
4,Terminate command execution: Ctrl + c
5,Terminal font enlargement: Ctrl + Shift + "+"
6,Terminal font reduction: Ctrl + "-"
8,practice
1,Create a command:
/home/tarena/Create directory under Directory: Guangdong Province
Create directory under Guangdong Province: Shenzhen
Create directory in Shenzhen: Bao'an District
2,Create a file under Bao'an District: Fuyong little sister
3,Create the following structure under the user's home directory:
Python
|
+-------+-------+------+
| | | |
Shanghai Wuchang Chengdu Shijiazhuang
catalogue catalogue Directory directory
9,rm : Delete file/catalogue
1,rm Options file/catalogue
-r : Delete all files/catalogue
-f : Force deletion,No hint
-i : Prompt before deleting(y representative yes,n representative no)
rm -rf file name/Directory name
5,text editor vi/vim 1,Format: vi file name 2,vi Three working modes of 1,Browse mode: enter at startup,Text cannot be edited 2,Insert mode(a/i/o) : Edit text 3,Command line mode(ESC -> shift + :) : Save exit.. 3,Text writing steps 1,vi file name 2,Press a/i/o : Edit text 3,Press ESC 4,Press shift + : --> Command line mode 5,wq : Save exit q! : Exit without saving w : preservation
6,Assignment 1 1,Create a file in the user's home directory: tarena.txt 2,stay tarena.txt Write the following contents to save and exit: Laugh up and go out,Are we Penghao people rm -rf Irrecoverable after deletion,Be careful when using Commonly used Linux Operating system: Ubuntu,CentOS,RedHat Linux Folders are called directories in mkdir -p Create a directory for recursion 3,see tarena.txt Content of cat tarena.txt 4,Switch to the directory above the current path 5,View the current path 6,Switch directly to the user's home directory 7,Assignment 2 1,Create a directory under the user's home directory: AID09 2,stay AID09 Create three directories: Linux Pbase AI 3,stay Linux Create 2 directories under Directory: day01,day02 4,stay day01 Create file under: day01.txt 5,stay Pbase Create 3 folders under: day01,day02,day03 6,stay day03 Create under directory day03.txt 7,delete Pbase Catalogue and Linux Lower day01 catalogue 8,Switch to user home directory
http://code.tarena.com.cn user name: tarenacode password: code_2013 route:/AIDCode/aid1809/
Day01 review
1,Test environment installation
1,Download materials: VMware,Ubuntu 16.04 iso Mirror file
2,Assembling a computer: files -> New virtual machine
3,Insert disc: CD/DVD -> Ubuntu 16.04***.iso
4,Power on: start this virtual machine
5,Installation software: Sogou input method Chrome browser ... ...
2,Linux
1,route
1,Absolute path: / start
2,Relative path:. .. ~ Directory name/......
2,pwd : Displays the current path
3,ls -la : View the contents of the directory
4,cd : Switch directory
1,cd /home/tarena/AID09
2,cd AID09/Linux
3,cd ~
4,cd
5,cd -
5,mkdir : Create directory
1,mkdir dir1 dir2 dir3
2,mkdir -p dir1/dir2/dir3
6,touch : create a file
touch file1 file2 file3
7,skill
1,Automatic replenishment: TAB key
2,Historical commands: keyboard up and down keys
3,Clean screen: Ctrl + l / clear
4,Terminal amplification: Ctrl + Shift + "+"
5,Terminal zoom out: Ctrl + "-"
8,rm -rf : Delete file/catalogue
9,text editor vi/vim
1,Three modes: browse mode, insert mode and command line mode
2,Operation steps
1,vim file name
2,Browse mode->Insert mode: a/i/o
3,Insert mode->Browse mode: ESC
4,Browse mode->Command line mode: Shift + :
5,Exit operation
wq!
q!
2. Python Basics
Day01 notes
2.1 Linux foundation
1. Linux commands
1,cp : Copy file/catalogue 1,Copy file: cp Source file path 2,Copy directory: cp -r Source directory path 3,cp *.txt /home/tarena/AID09 2,mv : shear/rename 1,Cut: mv File name path mv Directory name path 2,Rename: mv File name 1 file name 2 mv Directory name 1 directory name 2 3,practice 1,Create a file in the user's home directory: game.txt 2,use vim stay game.txt Write the following contents in: My big knife is already thirsty cp Command copy directory to add-r option mv There are two command functions,Cut and rename 3,take game.txt Cut to home directory AID09(If not, please create) 4,to game.txt Rename to: Dota.txt 5,hold AID09 Copy directory to /tmp 3,cat : view file contents(Output at terminal) cat file name 4,tar : Pack and compress 1,format tar -zcvf Compressed package name.tar.gz Compressed file required/catalogue -z : use gzip Compress the package -c : create package(create) -v : show details (verbose) -f : file 2,decompression tar -zxvf Compressed package name.tar.gz -C route -C : Specify the decompression path,Do not write. Extract to the current directory by default
3,practice 1,Create a directory under the user's home directory cd mkdir you and me 2,Create a file under the directory: file1 file2 file3 cd you touch file1 file2 file3 3,use vi stay file1 Write in: vi file1 Life is short,I use Python Wild road: ll tar xf ... 4,Pack and compress the directory into your.tar.gz cd tar -zcvf you.tar.gz you/ 5,Will you.tar.gz Cut to my directory mv you.tar.gz I/ 6,Will you.tar.gz Extract to current directory cd I/ tar -zxvf you.tar.gz
5,file right
1,see: ls -l file name
-rw-rw-r-- tarena tarena 2 A.txt
2,Leftmost column:-Representative type
1,d : catalogue
2,- : file
3,l : link(link)
3,jurisdiction
r : read
w : write(edit)
x : Executable
4,rwx Permission grouping
Group 1: file owner permissions
Group 2: file permissions of users in the same group
Group 3: other group users' permissions on files
scene(3 Users)
User 1: tarena Group: tarena : rw-
User 2: tarena2 Group: tarena : rw-
User 3: cloud Group: cloud : r--
6,chmod : Modify file permissions
1,Mode 1
1,Add relevant permissions to all users
chmod +x/-w/+rwx/-wx A.txt
2,Modify permissions for the specified group user
chmod u+x A.txt
chmod o+rwx A.txt
a : All users(all)
u : owner(user)
g : Same group user(group)
o : Other users(other)
2,Mode 2(Modify numerically)
chmod 644 A.txt : rw-r--r--
chmod 666 A.txt : rw-rw-rw-
r : 4
w : 2
x : 1
chmod 777 A.txt : rwxrwxrwx
3,practice
1,Create a file in the user's home directory: secret letter.txt
touch secret letter.txt
2,use vi Write to file:
My secret letter
When I look back, I smile and smile,Six palace pink without color
Spring nights are bitter and short, and the sun rises high,From then on, the king didn't come early
3,View secret letter.txt jurisdiction
ls -l secret letter.txt
4,Set file permissions to be readable, writable, and executable,Others have no authority
chmod 700 secret letter.txt
5,On the basis of 4, set the permission to be read-only for the same group of users
chmod 740 secret letter.txt
chmod g+r secret letter.txt
6,Remove the executable permission of the file
chmod -x secret letter.txt
7,Secret letter.txt Copy to under user's home directory AID09 in
cp secret letter.txt AID09/
2. Linux Advanced command
1,sudo : obtain root User's permission execution Linux command
cd /
touch A : Insufficient prompt permission
sudo touch A
## As long as the prompt permission is not enough, you can add it sudo ##
2,df -h : View disk usage
/dev/sda1 216G 16G 189G 8% /
3,top : Task Manager,see%CPU
4,ps -aux : View the of an application PID number
ps -aux | grep "firefox"
cat Fuyong little sister.doc | grep "hello"
5,kill -9 PID number
2.2 Python introduction
3. Python
1,Python brief introduction
1,application area
1,System operation and maintenance
2,Network programming
3,Artificial intelligence, robot
4,Web development
5,Cloud computing, big data
6,Crawlers, games, images ... ...
2,advantage
1,object-oriented
2,Open source and portable
3,Easy to learn and use, high development efficiency
3,shortcoming
Low execution efficiency
2,edition
1,Python2(2020 Stop maintenance in)
Python2.7
2,Python3
Python3.5(Teaching environment)
Python3.8(newest)
2.3 first Python program
4. My first Python program
1,File: hello.py Function: output at terminal hello world 2,function: python3 hello.py
5. Sublime code editor
1,multiline comment /Uncomment: Ctrl + / 2,preservation: Ctrl + s 3,Fallback: Ctrl + z 4,Select multiple cursors at the same time: Ctrl + Left click
6. Python interactive interpreter
1,get into: python3 2,sign out: exit() ,quit() ,Ctrl + d
2.4 Python Basics
7. Python data type
1,Number type
1,classification
1,integer int : 100 5 20
2,float float : 6.66 8.88 3.0
2,Representation of integers
1,decimal system
35 3*10**1 + 5*10**0= 35 50 666
2,Binary(0b start)
0b0000 # 0
0b0001 # 1
0b0010 # 2
0b01001000 # 1*2**6 + 1*2**3 = 72
3,hexadecimal(With 0 x start)
0 1 2 3 4 5 6 7 8 9 a b c d e f
0x11 # 1*16**1 + 1*16**0 = 17
0xFF # 15*16**1 + 15*16**0 = 255
0xA0 # 10*16**1 + 0*16**0 = 160
4,octal number system(With 0 o start)
0o177 # 1*8**2 + 7*8**1 + 7 = 12 7
0o11 # 1*8**1 + 1 = 9
2,character string
3,List, tuple ... ...
4,Boolean type bool : True ,False
5,Null value: None
8. Arithmetic operators
1,classification + - * / % : Remainder ** : exponentiation // : divide by, as long as an integer 2,priority(plus()control) ** * / % // + - 3,Examples The graduation salary of students is 10000.00 element,Up 20% a year%,What's your salary in ten years? 4,practice The watermelon in the supermarket is 7 yuan a piece,You have 100 yuan,How many watermelons can I buy,How much change? % //
9. Placeholder (string formatting)
1,format string % Variable name format string % (Variable 1,Variable 2) 2,%s Placeholder: String %d Placeholder: integer %f Placeholder: floating point number %.2f(Keep 2 decimal places)
3,practice 1,Define 2 variables,computer you,The values are: stone and cloth,Terminal output: Computer punch:Stone, you punch:Congratulations,You win! 2,Define 3 variables,name,gongsi,salary,Terminal output: ...Induction...company,Salary is...element 3,A circle has a radius of 3cm,Calculate the circumference and area of a circle pi : 3.14 The circumference of a circle with a radius of 3cm is:? centimeter The area of a circle with a radius of 3 cm is:? square centimetre Perimeter: 2 * 3.14 * 3 Area: 3.14 * 3 ** 2 4,Apples in the supermarket are 9 yuan a kilo,You have 100 yuan,How many kilograms of apples can I buy,How much money is left?(placeholder ) 5,If you're 23 now,365 days per year,How many Sundays have you spent?(placeholder ) 6,From 0 a.m:0:0 time,66666 seconds have passed,What time is it, please(placeholder )
10. Homework
1,Output graphics at terminal
*
***
*****
***
*
2,The scale in ancient China was 16 Liang and 1 jin,How many kilos is the current 216 liang,Write a program and print it out
3,Temperature conversion
Centigrade temperature = 5.0/9.0*(fahrenheit-32)
Kelvin temperature = Centigrade temperature + 273.15
Excuse me: what is the temperature from 100 Fahrenheit to Celsius?
What is the Kelvin temperature?
python_day01 review
command:
cp / cp -r Copy file/folder
mv move file/folder(Change name)
cat display the contents of a text file
tar Pack and compress $ tar -czvf folder
Unpack and compress $ tar -xzvf a.tar.gz
mkdir create folder
rmdir remove folders
touch create a file/Update the modification time of the file
chmod Modify file permissions
(read/write/implement)
rwx rwx rwx
sudo obtain root User authority, which is used to execute commands
df View disk
top Task Manager
ps see pid process
python
application area
python edition
python V3
python V2
python Implementation of:
$ python3 xxxxx.py
$ python3 <enter> # Interactive mode
>>>
>>> exit() / quit() / ctrl + d
python Data type of:
String, number, list....
Number type:
integer int
decimal system : -100 0 99 9999999 11
hexadecimal: 0x1234 0xABCD 0xabcd 0x11
octal number system : 0o12345670 0o11
Binary : 0b11
Floating point number float
3.14 .14 0.14 3. 3.0
314e-2 0.314e1 3.14E0
complex complex
(1 + 2j)
Boolean number bool
True/False
1 / 0
character string:
'' ""
Arithmetic operator:
+ - * / // % **
% Formatting of strings
Day02 notes
vscode (Visual Studio Code / Microsoft)
zoom ctrl + + / ctrl + -
notes ctrl + /
preservation ctrl + s (important)
start-up vscode Command of:
$ code <enter>
$ code file name<enter>
$ code Folder name<enter>
1. Variables
What are variables:
A variable is an identifier associated with an object
Variables can be bound to an object,And you can use this object by variable name
Naming method of identifier:
Start with a letter or underscore followed by a letter or number
explain:
Identifiers are case sensitive
Examples:
a A a1 bbbb set_age _ _abcd __abcde
a1b2
Illegal identifier:
1a 123 $ABC
python The keyword cannot be used as a variable name:
True, False, None, is, del, if,......
2. Assignment statements
Symbol =
grammar:
Variable name = expression
or
Variable name 1 = Variable name 2 = expression
or
Variable name 1, Variable name 2, ... = sequence
effect:
Create a variable and bind the data object
Change the bound data object of a variable
Examples:
a = 10
b = 20
c = a + b # c binding 30
a = b = c = 10000 # Change the binding relationship of three variables at the same time
# Bind to 10000 at the same time
x, y = 100, 200 # Bind 100 with x and 200 with y
practice:
Specify a rectangle with a long side length of 6(centimeter)
Short side length 4(centimeter)
Print out the perimeter and area of the rectangle
Description of assignment statement:
1. When the variable does not exist, the assignment statement creates the variable,At the same time, the variable
Bound to the object to the right of the assignment operator
2. When a variable exists, change the binding relationship of this variable
3. Only one object can be bound to a variable
4. Multiple variables can be bound to an object at the same time
as:
a = 100
b = a # b is also bound to the 100 bound by a
3. del statement
effect:
Used to delete variables and disassociate with objects. If possible, the
Release object
grammar:
del Variable name 1, Variable name 2, ...
View all variables in the current scope in interactive mode:
>>> help('__main__')
Examples:
a = 100
b = 200
x, y = 123, 456
del a
del b, x, y # Delete 3 variables at the same time
4. Automated memory management and reference counting:
Automated memory management and reference counting:Each object records several variable references(binding)oneself,When the number of references is 0, the object is destroyed. This automatic memory management method is called"Reference count"
5. is and is not operators
effect:
Judge whether two objects are the same object. When they are the same object
return True,Otherwise return False
is not And is The return value of is opposite
grammar:
x is y
x is not y
6. id function:
effect:
Returns the address of an object in memory
explain:
is Operator is based on id To judge
format:
id(object)
7. Small integer object pool:
CPython Medium, integer-5 To 256 always exist in the small integer object pool, will not be released, and can be reused
8. Compound assignment arithmetic operator
operator explain y += x Equivalent to y = y + x y -= x Equivalent to y = y - x y *= x Equivalent to y = y * x y /= x Equivalent to y = y / x y //=x equals y = y // x y %= x Equivalent to y = y % x y **= x Equivalent to y = y ** x
9. Comparison operator
< less than
<= Less than or equal to
> greater than
>= Greater than or equal to
== be equal to
!= Not equal to
grammar:
Left expression < Right expression
explain:
The comparison operator returns a Boolean value
Examples:
100 < 200
1 + 5 == 2 + 4
0 <= 60 <= 100
10. Constructor (creation) function of numeric object
Constructor of numeric object(establish) function
float(obj) Convert a string or number to a floating point number, if
If no parameters are given, 0 is returned.0
int(x, base=10) or int(x=0) Convert with number or string
Replace with an integer. If no parameters are given, 0 is returned
complex(r=0.0, i=0.0) Create a complex number with numbers(
The real part is r, Imaginary part is i)
bool(x) use x Create a Boolean value(True/False)
Syntax of function call:
Function name(Pass parameter list)
explain:
A function call is an expression that must return a reference to an object
Use relation(Or return None)
11. bool(x) returns a false value
value explain
None Null value
False Boolean false value
0 0.0 0j Number 0
------- Learn later------
'' character string
[] Empty list
() Empty tuple
{} Empty dictionary
....
practice:
Put the number 3.14 Use variable pi binding take pi Variable to integer i binding take pi Variables and i Variables are subtracted, and the result is variable f binding 1. judge f Is it equal to 0.14 2. Delete all variables (Do it in interactive mode)
12. Preset (built-in) numerical function
abs(x) take x Absolute value of
round(number[, ndigit]) Numerical"rounding",
ndigit Is the number of decimal places rounded to the right, and a negative number indicates to the left
Rounding
pow(x, y, z=None) amount to x**y or x**y%z
Examples: abs(-100) # 100 round(1234.56789) # 1235 round(1234.56789, 2) # 1234.57 round(1234.56789, 4) # 1234.5679 round(1234.56789, -2) # 1200.0 pow(5, 2) # 25 pow(5, 2, 10) # 5
13. help() function view the help of the function
>>> help(Function name) # View the help for the corresponding function
14. statement
A statement consists of some expressions. Usually, a statement can be executed independently Complete some things and form results Semicolons should be used when multiple statements are written in one line(;) separate See for example: code/statement.py
15. Explicit line Wrap:
When the sentence is too long, a line cannot be placed. Use \(Backslash)Perform an explicit line break See for example: statement2.py
16. Implicit line folding
The contents of all parentheses wrap, which is called implicit line break
Parentheses that can be used for implicit line breaks are:
() [] {}
17. Basic input and output functions
Basic input function input
effect:
Reads a string from a standard input setting(Does not contain line breaks)
format:
input('Prompt string')
explain:
Returns the string entered by the user
'Prompt string'Can be empty
See for example:
input.py
Basic output function print
format:
print(value, ..., sep=' ', end='\n',
file=sys.stdout, flush=False)
Outputs a series of values as strings to a standard output device
upper(Default to terminal)
Parameter options:
sep: Separator between two values(The default is a space' ')
end: Automatically append a string at the end after output(default
Line feed'\n')
file: Stream object(Default to sys.stdout)
flush: Output stream now
practice:
1. Enter two integers and use variables respectively x，y binding
1) Calculate the sum of these two numbers,And print the results
2) Calculate the product of these two numbers,And print the results
3) calculation x of y What is the power? And print
2. Enter the hours, minutes and seconds of the current time in three times
Then calculate the distance 0 a.m:0:0 How many seconds have passed
3. Calculation of three insurances and one fund:
What is the known contribution rate of social security:
project Individual payment proportion unit payment proportion
endowment insurance 8% 19%
employment injury insurance 0% 0.5%
medical insurance 2%+3 Yuan 10%
housing fund 12% 12%
Enter your social security base in Beijing(like: 5000)
Print individual payment details for you and the company,Total amount paid by individuals,
What is the amount paid by the unit and the money received by the state?
day02 review
python version of
python V2
python V3
python run:
1. at the command line prompt
$ python3 xxxx.py
2. Execute in interactive mode:
$ python3 <Enter>
>>>
>>> quit() / exit() / ctrl+d # quit
python Notes:
by # start to end of line
python Common data types:
Number type:
int
0, 999999999, -2, 0b1001, 0o11, 0x9
float
3.14, 0.314e1 314.0e-2
complex
1+2j
bool
True, False
string
list
....
null value object
None, Representative does not exist(nothing)
operator:
arithmetic operators:
+ - * / //(floor division) % (remainder) **(exponentiation)
comparison operator:
< <= > >= ==(equal) !=(not equal to)
assignment statement:
variable = expression
variable 1 = variable 2 = variable 3 = expression
variable 1, variable 2, variable 3 = sequence
The role is to create a variable to bind the result of the execution of the expression
del statement
del variable name
The effect is to delete the variable
is,is not operator
judge two objects id Is it the same
Compound assignment arithmetic operators:
+= -= *= /= //= %= **=
y +=x The effect is equivalent to y = y + x
function:
type conversion function:
float(obj)
int(x, base=10), int(x=0)
complex(r=0.0, i=0.0)
bool(x)
Syntax rules for function calls
Function name(parameter list)
A function call is an expression and must return a result(the result may be None)
Numeric function:
abs(x) Pick x the absolute value of
round(number[,ndigit]) Pick number approximation of
pow(x, y, z=None) # Find the remainder of x to the y power or x to the y power to z
Functions to view help:
>>> help('string')
>>> help(Function name)
Basic input and output functions:
input("prompt string") # Get the string entered by the user
print(value1, value2,..., sep=' ', end='\n'))
The function is to form a string into a number and print it on the screen terminal
Day03 Notes
1. if statement
if statement
question:
There are two statements:
print("this number is even")
print("this number is odd")
How to make only one of them execute???
if The role of sentences:
Let the program execute a certain statement or some statements selectively according to the conditions
grammar:
if truth expression 1:
statement block 1...
elif truth expression 2:
statement block 2...
elif truth expression 3:
statement block 3....
...
else:
statement block 4
illustrate:
elif Clause can have 0,1 one or more
else Clause can have 0 or 1 and can only be placed in if the end of the sentence
For example see:
if.py
practise:
Enter any integer
1) Determine if the number is greater than 100
2) Check if the number is less than 0
3) Determine if the number is within 50~150 between
(It is recommended to use one for each step if statement to implement)
if-elif-else For example see:
if_elif.py
practise:
1.Enter a quarter 1 ~ 4 Output which months in this quarter.
If the input is not 1~4 integer, prompting the user that you made a typo
2. Enter the month of the year(1~12),Output which quarter this month is in.
If you enter another number, it will prompt you to enter a wrong number
2. Nested if statements
if statement nesting
if The statement itself is a compound statement consisting of multiple clauses
if Statements can be nested as statements inside another compound statement
For example see:
if_embed.py
conditional expression
grammar:
expression 1 if truth expression else expression 2
effect:
According to the value of the truth expression(True/False) to decide to execute expression 1
or expression 2 and return the result
For example see:
if_express.py
practise:
1. Write a program that takes a number and uses if The statement calculates the number of
absolute value and print it
2. Write a program that inputs a number and uses a conditional expression to calculate the number
the absolute value of and print the result
3. pass statement
pass statement
effect:
Often used to fill in grammatical blanks
pass aka empty statement
grammar:
pass
For example see:
pass.py
4. Boolean operations
Boolean operations:
operator:
not and or
No and or
1.boolean not operation not
grammar
not x
effect:
right x perform boolean negation, such as bool(x) for True,then return False,
otherwise True
Example:
2.Boolean and operation and
grammar:
x and y
Note: x,y representative expression
effect:
Prefer to return false value objects,when x The boolean value of False , return x
otherwise return y
Example:
True and True # True
True and False # False
False and True # False
False and False # False
100 and 0.0 # 0.0
0 and 0.0 # 0
3.boolean or operation or
grammar:
x or y
effect:
Returns a truth value object first, when x for True return when x,otherwise return y
Example:
True or True # True
True or False # True
False or True # True
False or False # False
3.14 or 100 # 3.14
0 or 0.0 # 0.0
5. Sign operator
plus and minus operator
+(Positive sign) -negative
Note: unary operator(An element participates in the operation)
grammar:
+ expression
- expression
Example:
a = 5
b = -a # -negative
c = +a # Positive sign
print(a, b, c) # 5 -5 5
6. String str
string str
effect:
to record text(text)information
display method:
Anything enclosed in quotation marks in a non-comment is a string
' apostrophe
" Double quotes
''' triple single quotes
""" triple double quotation marks
A literal representation of the empty string
'' "" '''''' """"""
Expression method for literal value of non-empty string
'hello' "hello" '''hello''' """hello"""
7. The difference between single and double quotes
Double quotes within single quotes do not count as terminators Single quotes within double quotes do not count as terminators For example see: str.py
8. The role of triple-quoted strings
Triple-quoted strings can contain single and double quotes Newlines in triple-quoted strings are automatically converted to newlines'\n' For example see: str2.py
9. Implicit string literal concatenation
Implicit string literal concatenation
Example:
s = "I'm a teacher" 'my name is "Tarena"'
print(s) #
10. Use escape sequences to represent special characters
Use escape sequences to represent special characters Use the character backslash in string literals \ followed by some characters representing a special character such as: Convert word format Meaning \' represents a single quote \" represents a double quote \\ represents a backslash \n newline \r Return the cursor to the beginning of the line \f form feed \t horizontal tab \v vertical tab \b fall back \0 null character(character value is 0) \0oo oo character in two-digit octal \xXX XX character in two-digit hexadecimal representation \uXXXX Four-digit hexadecimal representation Unicode 16 character \UXXXXXXXX eight-digit hexadecimal representation Unicode 32 character
11.ASCII encoding table
ASCII code table
$ man ascii<Enter>
common ASCII coding
character decimal hex
'0' 48 0x30
'A' 65 0x41
'a' 97 0x61
12. The concept of sequence
sequence concept
Strings are sequences(orderly arrangement)
All sequences are available len(x) function to find its length
len(x) function
Returns the number of characters in a string
practise:
Use interactive mode to verify how many characters the following string has
1. '1234abcd' # 8
2. '5\'4"' # 4
3. '\"A\x34\056'# 4
4. '\a\bc\td\n' # 6
13.raw string (raw string)
raw string(raw string) Format: r'string content' r"string content" r'''string content''' r"""string content""" effect: let escape character backslash \ invalid Example: a = 'C:\newfile\test.py' print(a) print(len(a)) a = r'C:\newfile\test.py' print(a) print(len(a))
14. String operations:
String operations:
operator:
+ += * *=
+ The plus operator is used to concatenate strings
x = "ABCD"
y = "123"
z = x + y
print(z) # ABCD123
+= Used to concatenate the original string and the right string, and then use the variable to bind the new one
string
x = 'ABC'
y = '123'
x += y
print(x) # ABC123
* operator produces duplicate strings
x = "ABC" * 3
print(x) # ABCABCABC
Note: Strings can only be multiplied by integers
*= Generate repeated strings, and then use the original variable binding
x = '123'
x *= 2
print(x) # 123123
14. String comparison operations
String comparison operations
operator:
< <= > >= == !=
comparison rules:
Compare the two characters according to the encoding value in turn, if they are different, the comparison ends.
And return the comparison result, when the encoded value and length are exactly the same, the two characters
String the same
Example:
'A' < 'B' # True
'ABC' > 'ABB' # True
'ADC' < 'ABC' # False
'ABC' >= '123' # True
'AB' < 'ABC' # True
'abc' == 'ABC' # False
15.in, not in operator
in, not in operator
effect:
in Used in sequences, dictionaries, and sets to determine whether a value exists
in a container,return if exists True,then return False
not in and in operator returns the opposite
Format:
object in sequence
Example:
x = 'welcome to tarena!'
'to' in x # True
'hello' in x # False
'e t' in x # True
'abc' not in x # True
practise:
practise:
1. Beijing taxi meter:
Charges:
3 CNY 13 within a kilometer
Basic unit price 2.3 Yuan／kilometer(beyond 3 km)
empty driving fee: After more than 15 kilometers, 50 per kilometer will be charged for the unit price%of
empty driving fee(3.45 Yuan／kilometer)
Require: Enter the number of kilometers and print out the fee amount
2. Enter a student's grades for three subjects:
1) print out the highest score?
2) print out the minimum score?
3) print out the average score?
3. calculate BMI index(Body Mass Index) body mass index
Calculation formula:
BMI = weight(Kilogram)/height squared(Meter)
like:A 69 kg person and 173 cm tall, then
BMI = 69 / 1.73 ** 2 # got 23.05
Standard table:
BMI < 18.5 underweight
18.5 <= BMI < 24 normal weight
BMI >= 24 overweight
Require: Enter height and weight, print BMI value, and print the weight status
4. write a program．Print a rectangular box with a height of 4 lines
To display an integer, the integer represents the width of the rectangle, enter this rectangle
like:
Please enter rectangle width: 10
print as follows:
##########
# #
# #
##########
If you enter a larger number, the rectangle will be wider
day03 review:
if statement
Selectively execute one or some statements based on conditions
grammar:
if truth expression:
statement block 1
elif truth expression 2:
....
elif ....:
....
else:
statement block
first compound statement
if nesting of statements
if xxx:
if yyy:
if zzzz:
...
else:
....
else:
....
pass statement
Fill in syntax blanks
conditional expression
x + 1 if y > x else x + 2
Boolean operations:
and or not
unary operator:
+(Positive sign) -(negative)
-100
string str
"hello" 'ABC Chinese' 'A B C' '\n\t'
' " ''' """ beginning and end
The boolean value of an empty string is False
escape character:
'\n' '\r' '\\' '\'' '\"' '\t'
'\xXX' '\uXXXX' '\UXXXXXXXX'
ascii coding
len(x) find the length of the string
raw string
r'abc'
r"ab\n\rcd"
r'''abc'''
r"""abc"""
r'''ab
cd''' # Equivalent to 'ab\ncd'
String operations:
+ splicing * repeat n Second-rate += *=
< <= > >= == !=
"ABC" == "ABC"
"ABC" == "CBA" # False
in , not in
Day04 Notes:
1. Basic operations of strings
index index
python A string is an immutable sequence of characters
index value syntax:
string[integer expression]
illustrate:
python Sequences can be indexed(index) to access the objects in the sequence
python The forward index of the sequence starts at 0, and the second index is 1,at last
An index is len(s)-1
python The reverse index of the sequence is from-1 started,-1 represents the last,
-2 represents the second to last, and so on. the first is-len(s)
Example:
s = "ABCDE"
print(s[1]) # B
print(s[4]) # E
print(s[-1]) # E
print(s[-5]) # A
print(s[100]) # IndexError out of bounds
practise:
Write a program to input a string,print the following in the string
1. print the first character of this string
2. print the last character of this string
3. If the length of the string is odd, print the middle character
Note:
The function to find the length of a string is len(s)
2. Slice slice
slice slice
effect:
Take the corresponding elements from the string sequence and reconstitute a new string
grammar:
string[(start index b):(end index e)(:(step size s))]
Note:
Parentheses() The enclosed part means that it can be omitted
illustrate:
The start index is the position where the slice starts to be cut, and 0 represents the first element,1 represent
the second element,-1 represents the last....
end index is the end index of the slice(but not the end point)
The step size is the direction and offset that the slice moves after each time it gets the current element
1. No step size, equivalent to a step size of 1(Default is 1)
2. When the step size is a positive integer, take the forward slice:
The start index defaults to 0,The end index defaults to the last element
next position
3. Take the reverse slice when the step size is a negative integer:
When reverse slicing, the default starting position is the last element, ending
position is the previous position of the first element
Example:
s = "ABCDE"
a = s[1:4] # a---> "BCD"
a = s[:4] # 'ABCD'
a = s[1:] # 'BCDE' # Equivalent to s[1:5]
a = s[:] # 'ABCDE' # Equivalent to s[0:5]
a = s[1:1] # '' empty string
a = s[4:2] # '' null
a = s[0:5:2] # 'ACE'
a = s[4:0:-2] # 'EC'
a = s[4::-2] # 'ECA'
a = s[::-1] # 'EDCBA'
practise:
1. Write a program that takes a string and takes the first character of the string and
After the last character is removed, print out the processed string
2. Write a program, enter any string, and determine whether the string is a palindrome
A palindrome refers to a centrally symmetric text, such as:
Shanghai tap water comes from the sea
ABCCBA
3.Python operator precedence
Documentation see: python_base_docs_html/Python operator precedence.html
Documentation see:
python_base_docs_html/Python operator precedence.html
4. Functions that can be used for strings in python3
python3 functions that can be used with strings in:
len(x) return string length
max(x) Returns the character with the largest string encoding value
min(x) Returns the character with the smallest encoded value in the string
String encoding conversion function:
ord(c) return a character c of unicode encoded value
chr(i) return i the character corresponding to this value
Example:
x = ord('A') # x = 65
c = chr(66) # c = 'B'
practise:
1. Write a program, input a string, if the string is not empty, put the first
The encoded value of a character is printed out
2. Write a program that takes an integer(0~65535)，print this value
corresponding character
5. Functions for converting integers to strings
Integer to String function:
bin(i) convert integer to binary string
oct(i) Convert integer to octal string
hex(i) Convert integer to hex string
String construction(create)function:
str(obj) convert object to string
Example:
'123' + 456 # error
'123' + str(456) # result '123456'
6. String methods commonly used in python3 (method)
python3 String methods commonly used in(method)
method call syntax:
object.method name(method parameter)
Example:
'abc'.isalpha() # return True
'123'.isalpha() # return False
123.isalpha() # error
See the documentation for the method:
python_base_docs_html/str.html python_base_docs_html/str.html
practise:
enter a string:
1. Determine how many spaces there are in the character you entered
2. Remove the left and right blank characters of the original string and print out valid characters
number
3. Determine if your input is a number,
If it is a number, determine whether the number entered by the user is greater than 100
7. String formatting expressions
1.string formatting expression
effect:
Generate a string in a certain format
operator:
%
syntax format:
format string % parameter value
format string % (parameter value 1, parameter value 2, parameter value 3, ...)
illustrate:
The format string starts with%The character at the beginning is a placeholder, and the position of the placeholder will be
replace with parameter value
Example:
fmt = "name: %s, age: %d"
s2 = fmt % ("Tarena", 15)
fmt2 = "age: %d"
s3 = fmt2 % 35
2.placeholder type code in format string
Placeholders and Typecodes meaning
%s string, use str(x) function transformation
%r string, use repr(x) function transformation
%c Integer to single character
%d decimal integer
%o octal integer
%x hex integer(character a-f lower case)
%X hex integer(character A-F capital)
%e Exponential floating point number(e lower case) like: 2.9e8
%E Exponential floating point number(E capital) like: 2.9E8
%f,%F floating point decimal
%g,%G Automatic conversion of decimal form floating point or exponential floating point
%% equivalent to a%character
3.Format syntax between placeholders and type codes
% [ - + 0 width.precision ] type code
- Align left(The default is right-aligned)
+ Show positive sign
0 Zero padding in the left blank
width The width of the entire data input
Precision How many digits after the decimal point are retained(Default is 6 bits)
Example:
"%10d" % 123 # ' 123'
"%-10d" % 123 # '123 '
"%10s" % "abc" # ' abc'
'%-5s' % 'abc' # 'abc '
'%05d' % 123 # '00123'
'%+05d' % 123 # '+0123'
'%7.3f' % 3.1415926535 # ' 3.142'
practise:
Enter three lines of text, and align the three lines of text to the right with a width of 20 characters
show
like:
Please enter line 1: hello world
Please enter line 2: abcd
Please enter line 3: aaaaaaa
The print result is as follows:
hello world
abcd
aaaaaaa
Think after you have finished:
Can the display be right-aligned by the length of the longest string?(left padding
space)
8. Loop statement:
loop statement:
while statement
for statement
question:
enter an integer n,Write the program to print as follows n line text:
This is line 1
This is line 2
This is line 3
...
This is the first n Row
while statement:
effect:
Execute a statement or multiple statements repeatedly based on certain conditions
grammar:
while truth expression:
statement block 1(This part of the statement may be repeated many times)
else:
statement block 2
illustrate:
1. Execute the truth expression first,get boolean value True or False
2. If the value of the truth expression is True,then execute block 1,after that
Return to step 1 and repeat the test for the value of the truth expression
3. If the value of the truth expression is False,then execute else clause part
statement block 2,then end this while execution of the statement
Note: else clause part can be omitted(same if Statements like)
For example see:
while.py
practise:
1. Enter three lines of text to center them in a box
as input:
hello!
I'm studing python!
I like python!
Shows as follows:
+---------------------+
| hello! |
| I'm studing python! |
| I like python! |
+---------------------+
2. use while loop print 1 ~ 20 the integer(Can print multiple lines)
3. use while loop print 1 ~ 20 Integer, printed on one line
Separate each number with a space
1 2 3 4 5 6 .... 18 19 20
4. use while loop print 1 ~ 20 The integers, 5 are printed per line,
print 4 lines,like:
1 2 3 4 5
6 7 8 9 10
...
5. enter an integer n,prints a width and height of n character rectangle
like:
please enter: 4
Print:
####
# #
# #
####
like:
please enter: 6
Print:
######
# #
# #
# #
# #
######
day04 review:
string index, slice
index
take out a character
slice:
Take out some characters and reconstitute a string
index syntax:
string[integer expression]
Slice syntax:
string[start index:end index:step size]
function:
chr(integer) # Convert to string (contains only one character)
ord(a character) # Convert to integer encoded value
bin(i)
oct(i)
hex(i)
str(obj) convert object to string
Common methods for strings:
S.isdigit()
S.isalpha()
S.islower()
S.isupper()
S.isspace()
S.center(width, fill=' ')
S.count(sub, start, end)
S.find(...)
S.strip([char]) / S.lstrip() S.rstrip()
S.upper() / S.lower()
S.replace(old, new)
S.startswith(string) / S.endswith(string)
>>> help(str)
string format expression
"Name: %s, gender:%s， age:%d" % ("Xiao Zhang", "male",20)
Common placeholders and type codes:
%s
%d
%f %7.2f %-7.2f %+7.2f %07.2f
while statement (loop statement)
grammar:
while truth expression:
block of statements that may be executed repeatedly
else:
statement block 2
practise:
1. enter an integer n value representing the end,find the sum of the following expressions
1 + 2 + 3 + 4 + .... + (n-1) + n the sum
like:
please enter: 100
Print:
5050
Day05 Notes:
1. Notes on while statement:
while Statement Notes:
1. To control the value of the truth expression of the loop to prevent infinite loops
2. Often loop conditions are controlled by loop variables inside truth expressions
3. Usually changing the loop variable inside the statement
1. To control the value of the truth expression of the loop to prevent an infinite loop
2. Loop variables are usually used in truth expressions to control loop conditions
3. Usually change the loop variable inside the statement
2. Nested while statements:
while statement nesting:
while sentences are sentences,Like other statements, it can be nested into
in any compound statement
signal:
while truth expression:
....
while truth expression 2:
....
else:
...
...
else:
...
For example see:
while_embed.py
practise:
enter an integer n,Print a square of the specified width
like:
please enter: 5
Print:
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
1 2 3 4 5
like:
please enter: 3
Print:
1 2 3
1 2 3
1 2 3
3.break statement
break statement question: If you do not want to continue the execution of the loop statement during the loop,How to do? effect: for loop statement(while,for statement)middle,Used to terminate the current loop statement execution. illustrate: when break After the statement is executed,this loop statement break Statements after that will no longer be executed break Statements are usually if Combination of statements break statement terminates the loop,loop statement else clause's statement will not execute break statement can only terminate the execution of the current loop statement,If there are loops nested Time,Does not break out of nested outer loops break statement can only be used in a loop statement(while,for statement)internal use of For example see: break.py
9. Infinite loop
infinite loop An infinite loop is a loop in which the loop condition is always established Infinite loop can usually be used break statement to terminate the loop infinite loop else clause never executes
Let the user enter some arbitrary integer,End input when negative number is entered
When the input is complete,print the sum of these numbers you entered
like:
please enter: 1
please enter: 2
please enter: 3
please enter: 4
please enter: -1
Print: 10
10. Loop Statement
loop statement:
while statement
for statement
for statement
effect:
The data elements used to iterate over the iterable object
Iterable objects are objects that can sequentially obtain data elements
like:
string,list,tuple,range Objects returned by functions, etc.
grammar:
for variable list in iterable object:
statement block 1(Here is a block of statements that may be executed repeatedly)
else:
statement block 2
illustrate:
when used in circulation break when the loop is terminated,else clause part
sentence will not execute
else clause part can be omitted
For example see:
for.py
practise:
practise:
Enter any string
1) Count the number of spaces in a string
2) Calculate the number of Chinese characters in a string
(Note: The encoding value of Chinese characters must be greater than 128,available ord judge)
11.range() function
range() function:
range(stop) used to generate 0~stop integer in range,until stop for
end(does not contain stop)
range(start, stop[,step]) used to generate start~stop Area
integer in the interval,until stop until(does not contain stop),
every integer interval step
See the format for details:
>>> help(range)
effect:
Used to create an iterable that yields a sequence of integers(Also called a sequence of integers
Builder)
signal:
range(4) generate 0, 1, 2, 3
range(3, 6) Build 3, 4, 5
range(1, 10, 2) Generate 1, 3, 5, 7, 9
range(5, 0, -1) Build 5, 4, 3, 2, 1
range(5, 0, -2) Build 5, 3, 1
range(4, 0) generate empty
For example see:
range.py
practise:
1. print 1 ~ 20 integers, printed on one line(use for Statement implementation)
2. Calculate 1 + 2 + 3 + 4 + ..... + 99 + 100 the sum
(use for and range accomplish)
3. Calculate 1 + 3 + 5 + 7 + .... + 97 + 99 the sum
(use for Statement implementation)
for statement nesting:
Example:
for x in "ABC":
for y in "123":
print(x + y)
12.continue statement
continue statement
question:
How to stop the program from going down and start a new loop again?
effect:
for loop statement(while，for), no longer execute this loop
continue After the statement, start a new loop again
illustrate:
1. exist while execute in statement continue statement, will jump directly to
while At the truth expression of the statement, re-evaluate the loop condition
2. exist for execute in statement continue statement, which will start from the iterable object
loop again after taking the next data-bound variable in
For example see:
continue.py
practise: beg:1 ~ 100 All in between cannot be 2, 3, 5, 7 sum of divisible numbers
Loop summary:
while statement
for statement
string str
range() the object returned by the function
break statement
continue statement
question:
container
How to temporarily store the data calculated by the computer in one place, and at the same time
Easy to add, delete, modify, view and other operations
13. List list
1. List creation and constructor
list list
A list is a container
Lists are sequence containers that can be changed
Create an empty list literal
L = [] # L binds a newly created empty list
A literal that creates a non-empty list:
L = [1, 2, 3, 4]
L = ["Beijing", "Shanghai", "Shenzhen"]
L = [1, "two", 3.14, "Four"]
L = [1, 2, [3.1, 3.2, 3.3], 4]
List construction(create)function list
list() Creates an empty list, equivalent to[]
list(iterable) Create a list with iterable objects
Example:
L = list() # L bind empty list
L = list("hello") #L binding['h','e','l','l','o']
L = list(range(10)) # L binding [0,1,2,3...9]
2. Operations on lists
Operations on lists:
arithmetic operators
+ += * *=
Example:
+ plus sign for concatenating lists
x = [1, 2, 3]
y = [4, 5, 6]
z = x + y # z = [1, 2, 3, 4, 5, 6]
+= Used for splicing the original list with the iterable object on the right,bind list with variable
grammar:
x += iterable object
like:
x = [1, 2, 3]
y = [4, 5, 6]
x += y # x bind [1, 2, 3, 4, 5, 6]
x =
* generate duplicate lists
*= repeat the original list n use the original variable binding again
x = [1, 2] * 3 # x =[1, 2, 1, 2, 1, 2]
x = [1, 2]
x *= 2 # x = [1, 2, 1, 2]
practise:
1.enter an integer n,This integer represents the length of the right-angled sides of the triangle
according to integer n Print the following four triangles
please enter: 3
print as follows:
1)
*
**
***
2)
*
**
***
3)
***
**
*
4)
***
**
*
2. write a program,Enter any integer,Check if this integer is a prime number(prime)
Prime number(also called prime numbers), positive integer only divisible by 1 and itself
like: 2 3 5 7 11 13 17 19
hint:
by exclusion,when judging x Whether it is a prime number,just let x divided by
2, 3, 4, ... x-1 ,as long as there is one divisible,but x no
Prime number,otherwise x is a prime number
3. Enter a positive integer representing the width and height of the square,print the following square
like
please enter: 5
Print:
1 2 3 4 5
2 3 4 5 6
3 4 5 6 7
4 5 6 7 8
5 6 7 8 9
like
please enter: 3
Print:
1 2 3
2 3 4
3 4 5
day05 review
loop statement
while statement
for statement
while grammar:
while truth expression:
statement block 1
else:
statement block 2
for grammar
for variable name in iterable object:
statement block 1
else:
statement block 2
iterable object:
str
range() the returned object
list list
range(start integer,end integer,step size)
range(start integer,end integer)
range(end integer)
break statement
terminate the current loop
break after execution,loop statement else The statement in the clause will not be executed
continue statement
start a new cycle
for while and for Statement jump position is different
list list
How to create a list
[]
[1, 2, 3, 4]
[1, 2, [3, [4, 5]], 6]
Constructor
list()
list(iterable object)
Operations on lists:
+ += * *=
+= operator is equivalent to appending data to the end of the original list
L = [1, 2]
print(id(L))
L += [3] # is not equivalent to L = L + [3]
print(id(L)) # id does not change
Day06 Notes:
3. List comparison operations
List comparison operations:
operator:
< <= > >= == !=
illustrate:
The comparison rules for lists are the same as for strings
Lists require that every two elements be compared in turn,Otherwise there will be a type error
Example:
[1, 2, 3] < [1, 2, 4] # True
[1, 2, 3] != [1, 2, 4] # True
["One", "Two"] < ["1", "2"] # False
[1, 'Two'] > ['Two', 1] # TypeError
[1, "two", 3.14] < [2, "2", 1] # True
4. The in / not in operator for lists
list in / not in operator
Check if a value exists in the list, and return if it exists True,
otherwise return False
the same string in operator like
Example:
x = [1, 'Two', 3, "Four"]
3 in x # True
"3" in x # False
10 not in x # True
5. Indexing operations on lists
Indexing operations on lists:
1.index value
grammar:
x = list[integer expression]
usage:
equivalent to the index of the string(Also divided into forward index and reverse index)
2.index assignment
Lists are mutable sequences,Elements in a list can be changed by index assignment
grammar:
list[integer expression] = expression
Example:
x = [1, 2, 3, 4]
x[2] = 1 + 2.14 # Changed the value of the third element
print(x)
6. List slice operation
Slicing operations for lists
1.slice value
list[start index:end index:step size]
The value of the slice of the list is to take the desired elements from the original list and form a new one
new list
Example:
L = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
y = L[1:10:2] # y = [1, 3, 5, 7, 9]
2.Slice assignment operation
effect:
You can change the arrangement of the original list,can be inserted,and modify data
grammar:
list[slice] = iterable object
illustrate:
assignment operator for slice assignment(=)The right side of must be an iterable
Example:
L = [2, 3, 4]
L[0:1] = [1.1, 2.2] # L=[1.1, 2.2, 3, 4]
L[0:2] = [2] # L = [2, 3, 4]
L[1:2] = [3.1, 3.2] # L = [2, 3.1, 3.2, 4]
L = [2, 3, 4]
L[1:1] = [2.1, 2.2] # L = [2, 2.1, 2.2, 3, 4]
L[0:0] = [0, 1] # L = [0, 1, 2, 2.1 ....]
L = [2, 3, 4]
L[3:3] = [5, 6] # L = [2, 3, 4, 5, 6]
L = [2, 3, 4]
L[1:2] = "AB" # L = [2, 'A', 'B', 4]
L[1:3] = range(7, 10) # L = [2, 7, 8, 9, 4]
3.Notes on Slicing:
Assignment to slices with stride not equal to 1,the iterable on the right-hand side of the assignment operator
number of elements provided,Must be equal to the number of segments cut out by the slice
L = [1, 2, 3, 4, 5, 6]
L[::2] = "ABC" # correct
L[::2] = "abcd" # Incorrect
1.del statement
del statement
Can be used to delete elements of a list
grammar:
del list[integer expression]
del list[slice]
Example:
L = [1, 2, 3, 4, 5, 6, 7, 8]
del L[-1] # L = [1, 2, 3, 4, 5, 6, 7]
del L[1::2] # L = [1, 3, 5, 7]
practise:
already has a list:
L = [3, 5]
Working with indexing and slicing,Change the original list to:
L = [1, 2, 3, 4, 5, 6]
reverse the list,The result is as follows:
L = [6, 5, 4, 3, 2, 1]
then remove the last element,The result is as follows :
L = [6, 5, 4, 3, 2]
practise:
practise:
write a program.Let the user enter many positive integers,End input when negative number is entered
Store the numbers entered by the user in a list
1. print a list of numbers
2. find the average of these numbers
3. find the largest of the numbers
like:
please enter: 1
please enter: 2
please enter: 99
please enter: 100
please enter: -1
print as follows :
list is: [1, 2, 99, 100]
The average is: 55.5
The maximum number is: 100
2. Functions of sequences commonly used in python3
len(x) Returns the length of the sequence
max(x) Returns the maximum element of the sequence
min(x) Returns the smallest element in the sequence
sum(x) Returns the sum of all elements in the sequence(Elements must be of numeric type)
any(x) truth test.Returns if one of the values in the list is true True
all(x) truth test.Returns if all values in the list are true True
Example:
L = ["Beijing", 1, 123]
print(len(L)) # 3
L = [8, 3, 6, 2]
print(max(L)) # 8
print(min(L)) # 2
print(sum(L)) # 19
3. List methods commonly used in python3 (method)
Documentation see:
python_base_docs_html/list.html
>>> help(list)
practise:
write a program,Let the user enter many positive integers,When entering a number less than zero
end input
1) print the largest of these numbers
2) print the second largest of these numbers
3) delete the smallest number
4. shallow copy and deep copy deep copy
1. Shallow copy
shallow copy
Shallow copy refers to the process of copying,Copy only one level of variables,will not copy deep
The copy process of the object bound by the variable
like:
L = [3.1, 3.2]
L1 = [1, 2, L]
L2 = L1.copy() # shallow copy
print(L1) # [1, 2, [3.1, 3.2]]
print(L2) # [1, 2, [3.1, 3.2]]
L2[2][0] = 3.14
print(L1) # [1, 2, [3.14, 3.2]]
print(L2) # [1, 2, [3.14, 3.2]]
2. Deep copy
deep copy deep copy
like:
import copy # import copy module
L = [3.1, 3.2]
L1 = [1, 2, L]
L2 = copy.deepcopy(L1) # deep copy
print(L1) # [1, 2, [3.1, 3.2]]
print(L2) # [1, 2, [3.1, 3.2]]
L2[2][0] = 3.14
print(L1) # [1, 2, [3.1, 3.2]]
print(L2) # [1, 2, [3.14, 3.2]]
3. The difference between shallow copy and deep copy
1.Shallow copy only copies the reference address to an object, not the object itself, the old and new objects still share the same memory.
2.But deep copying will create another identical object, the new object does not share memory with the original object, and modifying the new object will not change the original object.
Shallow copy only copies the properties of one level of object, while deep copy recursively copies all levels.
import copy as cp
L=[1,[2,3]]
L1=cp.copy(L) #Shallow copy: just reference, and will not open up new memory space,
L1 and L point to the same memory space. L Change,L1 also locks in changes.
L2=cp.deepcopy(L) #Deep copy: It will re-create a memory space for data, and changes in L will not affect L2.
5. List and String Comparison
list to string comparison:
1. Both lists and strings are sequences,There is a sequence relationship between elements
2. Lists and strings have the same operations: + += * *= < > in ...
3. Strings are immutable sequences, lists are mutable sequences
4. Each element of a string can only store characters, while a list can store any type
Elements
5. Both lists and strings are iterable objects
6. String text parsing methods split and join
Text parsing methods for strings split and join
S.split(sep=None) use string sep split as delimiter s
String, returns a list of split strings;When no parameters are given
When counting, use a whitespace character as a delimiter
S.join(iterable) Generates a medium from the strings in the iterable object
Room use S delimited string
Example:
s = 'Beijing is Capital'
L = s.split(' ') # L = ['Beijing', 'is', 'Capital']
s2 = "##".join(L) # s2 = "Beijing##is##Capital"
practise:
has string "hello"
generate new string:
'h e l l o' and 'h-e-l-l-o'
s1 = ' '.join('hello')
s2 = '-'.join('hello')
7. List comprehension
1.list comprehension list comprehesion
List comprehensions are expressions that create lists from iterable objects
effect:
Create a list
grammar:
[ expression for variable in iterable object]
or
[ expression for variable in iterable object if truth expression]
Example:
generates a value of 1~9 list of squares
L = [x**2 for x in range(1, 10)]
# L = [1, 4, 9, 16 .... 64, 81]
# Generate a list of squares of values 1 to 9 (as long as there are odd squares)
L = [x**2 for x in range(1, 10) if x % 2 == 1]
# L = [1, 9, 25, 49, 81]
# The above list comprehension can be rewritten as:
L = []
for x in range(1, 10):
if x % 2 == 1:
L.append(x**2)
2.List Comprehension Nested Syntax:
[ expression
for variable 1 in iterable object 1 if truth expression 1
for variable 2 in iterable object 2 if truth expression 2
.....]
like:
L = [x + y for x in "ABC" for y in "123"]
# L = ['A1', 'A2', 'A3', 'B1', 'B2', 'B3',
'C1', 'C2', 'C3']
practise:
1. There are some numbers in the list,like:
L = [1, 3, 2, 1, 6, 4, 2, ..... 98, 82]
1) Store numbers that appear in a list into another list L2 middle
Require:
Numbers that appear multiple times can only be found in L2 keep a copy(deduplication)
2) Store numbers that appear twice in a list in L3 List,exist L3 List
keep only one
2.generate a list,beg x squared+1 list of,Skip results divisible by 5
number, (Note: 0 <= x <= 100)
3. put 0 ~ 100 All prime numbers between are stored in a list
which is: L = [2, 3, 5, 7, 11, ..... 97]
day06 review:
list list
How the list is created:
literal value
[], [1,2,3,4]
Constructor:
list() list("ABCD")
derivation:
[x**2+1 for x in range(10)]
Operations on lists:
+ += * *=
< <= > >= == !=
in, not in
The index value and slice value rules are equivalent to the rules for strings
Index assignment and slice assignment
list[integer expression] = expression
list[slice] = iterable object
L[1:2] = range(10)
serial correlation function:
len(x) --> len(iterable object)
max(x) --> max(iterable object), max(value 1,Numeric 2,...)
min(x)
sum(x) --> sum(iterable object)
any(x) --> any(iterable object)
all(x) --> all(iterable object)
List of commonly used methods:
L.append(x) append
L.insert(index, data object)
L.extend(iterable object)
L.remove(data object)
L.pop([integer index])
L.clear()
L.count(data object)
L.index(data object) Returns the position of the first occurrence
L.sort(reverse=False) sort
L.reverse() reverse
String parsing method:
S.split(sep=None)
S.join(iterable object)
list comprehension:
[x**2 for x in range(10)]
[x**2 for x in range(10) if x > 5]
[x*y+2 for x in range(10) for y in range(20)]
deep copy and shallow copy
L = [1, 2, 3, [4, 5, 6]]
L2 = L # Do not copy, give L's reference to L2
L3 = L.copy() # shallow copy
import copy
L4 = copy.deepcopy(L) # deep copy
Day07 Notes:
1. Tuple tuple
tuple tuple
Tuples are immutable sequences,same list Same,Tuples can store any type
data container
Tabular methods for tuples:
with parentheses() bracket,Surround individual elements with a comma(,)distinguish a single
object or tuple
Creates a literal value of an empty tuple:
t = () # Create an empty tuple bound with t
A literal that creates a non-empty tuple
t = 200, # Create a tuple with only one number 200 with binding
t = (20,)
t = (1, 2, 3)
t = 100, 200, 300
Bad example of created tuple:
t = (20) t bind integer 20,not a tuple
x, y, z = (100, 200, 300) # sequence assignment
x, y, z = 100, 200, 300
x, y, z = [100, 200, 300]
x, y, z = "ABC" # Sequence assignment, not tuple
x, y = y, x # Swap the bindings of two variables
type(x) function return x type
tuple constructor tuple
tuple() generates an empty tuple,Equivalent to()
tuple(iterable) Generate a new tuple with an iterable object
Example:
t = tuple()
t = tuple("ABC")
t = tuple(range(1, 10, 3))
operations on tuples:
+ += * *=
t = (1, 2, 3) + (4, 5, 6) # t=(1,2,3,4,5,6)
t = (1,2,3)
t += (4,5,6) # t = (1,2,3,4,5,6)
t = (1,2) * 3 # t =(1,2,1,2,1,2)
t = (1,2)
t *= 3
comparison operation:
< <= > >= == !=
The comparison rules are exactly the same as the comparison rules for lists
in / not in operator
equivalent to a list in / not in operator
Indexing and Slicing
The rules for indexing and slicing are exactly the same as for lists
Note: Tuples do not support index assignment and slice assignment
tuple methods
see documentation:
python_base_docs_html/tuple.html
Sequence-related functions can also be used in tuples
len(x), max(x), min(x),
sum(x), any(x), all(x)
2. Dictionary dict
1. Dictionary dict (create)
dictionary dict
what is a dictionary
1. A dictionary is a mutable container,Can store any type of data
2. Each data in the dictionary is represented by"key"(key) indexed,instead of
like sequence(str,list,tuple)can be indexed with integers
3. The data in the dictionary has no sequence relationship,Dictionary storage is unordered
4. The data in the dictionary starts with the key(key)-value(value)store the form
5. Dictionary keys cannot be repeated,and can only use immutable types as dictionary keys
The literal way of creating a dictionary:
The dictionary is represented by{} bracket,with a colon(:) Delimited key-value pairs,each key
Separate value pairs with commas
Create empty dictionary:
d = {}
Create a non-empty dictionary:
d = {"Name": "tarena", "age": 15}
d = {"one": 1, "two": 2}
d = {1: "One", 2: "two", 3: [1,2,3]}
d = {"a": list(range(10))}
d = {"a": {"b": 100, "c":[1, 2, 3]}}
constructor that creates a dictionary dict:
dict() # produces an empty dictionary equivalent to {}
dict(iterable) Create a list with iterable objects
dict(**kwargs) Generate a dictionary in the form of keyword arguments
Example:
d = dict()
L = [ (1, 2), [3, 4], "AB" ]
d = dict(L) # {1: 2, 3: 4, 'A': 'B'}
d = dict(name="tarena", age=15)
# d = {'age': 15, 'name': 'tarena'}
Dictionary keys must be immutable values
There are four types of variable:
list(list), dict(dictionary), set(gather),
bytearray(byte array)
(In addition to the above four others are immutable types)
2. Basic dictionary operations
Basic dictionary operations
1.dictionary key index
grammar:
dictionary[key]
effect:
Get the value corresponding to the key of the dictionary with the key
Example:
d = {'name': 'tarena', 'age': 16}
print(d['name'], "age is", d['age'])
2.Add and modify elements of a dictionary
grammar:
dictionary[key] = value
illustrate:
When the key does not exist,Create key,and let the key bind the corresponding value
key exists,Modify the value of a key binding
Example:
d = {}
d['name'] = "Xiao Zhang" # Add a key-value pair
d['age'] = 20 # Add a key-value pair
d['age'] += 1 # Modify the value corresponding to the 'age' key
practise:
write a program,Let the user enter a person's information twice:
Information contains: name and phone number
Let users have multiple personal information,End input when input name is empty
Store the data entered by the user in a dictionary
name as key, phone number as value
Finally print the dictionary storing the data
like:
Please type in your name: Xiao Zhang
Please enter phone: 13888888888
Please type in your name: Xiao Li
Please enter phone: 13999999999
Please type in your name: <Enter>
Print:
{"Xiao Zhang": 13888888888, "Xiao Li": 13999999999}
3.remove dictionary element
del statement
grammar:
del dictionary[key]
Example:
d = dict(name="Xiao Zhang", age=20)
del d['age']
print(d) # {'name': 'Xiao Zhang'}
4.Dictionary key judgment in , not in operator
Can use in operator to determine if a key exists in the dictionary,if it exists
then return True, otherwise return False
not in return value with in on the contrary
E.g:
d = {'name' : 'tarena', 'age': 15}
'name' in d # True
15 in d # False
'age' not in d # False
practise:
programming,fulfill the following requirements:
1. Form the following data into a dictionary seasons
key value
1 ====> 'Spring has 1,2,3 moon'
2 ====> 'There are 4 in summer,5,6 moon'
3 ====> 'Fall has 7,8,9 moon'
4 ====> '10 in winter,11,12 moon'
2. Let the user enter an integer representing the quarter,print the corresponding quarter
information,If the information entered by the user does not exist in the dictionary,prompt the user
'information does not exist'
3. Iterative access to the dictionary
iterative access to the dictionary
Dictionaries are iterable objects,Dictionaries can only have iterative access to keys
Example:
d = {0:'zero', 5:'Wu', 1:'one', 2:'two'}
for n in d:
print(n) # 0, 1, 2, 5
functions that can be used with dictionaries:
len(x) Returns the number of key-value pairs in the dictionary
max(x) Returns the maximum value of the keys of the dictionary
min(x) Returns the minimum value of the keys of the dictionary
sum(x) Returns the sum of all keys of the dictionary
any(x) truth test,Test only on keys,As long as there is a key with a true value
the result is True
all(x) truth test,The truth-valued result for all keys is True
Example:
d = {0:'zero', 5:'Wu', 1:'one', 2:'two'}
len(x)
...
4. The dictionary method
dictionary method
Documentation see:
python_base_docs_html/dict.html
Example:
d = {0:'zero', 5:'Wu', 1:'one', 2:'two'}
for t in d.items():
print(t) # (0, 'zero'), (1, 'one'), (2, 'two'), (5, 'wu')
for k, v in d.items():
print("key is", k, 'value is', v)
practise:
Enter a string, print out the characters that have appeared in the string and the characters that have appeared in the string
the number of times
like:
enter: abcdabcaba
print as follows:
a: 4 Second-rate
b: 3 Second-rate
d: 1 Second-rate
c: 2 Second-rate
Note: Print order is not required
5. Dictionary comprehension
dictionary comprehension
Dictionary comprehensions are expressions that use iterable objects to create dictionaries
grammar:
{key expression: value expression for variable in iterable object
[if truth expression]}
Note: []The content of the representative can be omitted
Example:
generate a dictionary: key is number 0~９, value is the square of the key
as generated {0: 0, 1:1, 2:4, 3: 9, ... 9:81}
d = {x: x**2 for x in range(10)}
print(d)
dictionary comprehension nesting
The syntax is the same as list comprehension nesting
practise:
A list of known strings like:
L = ['Tarena', 'XiaoZhang', 'xiaowang']
Generate the following dictionary:
d = {'Tarena':6, 'XiaoZhang':9,
'xiaowang':8}
practise:
Nos = [1001, 1002, 1005, 1006]
names = ['Tom', 'Jerry', 'Spike', 'Tyke']
Try to generate the following dictionary:
d = {1001: 'Tom', 1002: 'Jerry',
1005: 'Spike', 1006: 'Tyke'}
Answer:
d = {Nos[i]: names[i] for i in range(4)}
6. Dictionary VS List
dictionary VS list
1. are mutable containers
2. The indexing method is different, the list is indexed by integer, and the dictionary is indexed by key
3. The storage of lists is ordered, and the storage of dictionaries is unordered
4. Insertion, deletion, modification of dictionaries may be faster than lists(important)
question:
L = [1, 3, 5, 8, 10]
for x in L:
L.remove(x)
print(L) # [3, 8]
practise:
1. Generate the first 40 Fibonacci numbers (Fibonacci sequence)
1 1 2 3 5 8 13 21 ....
Require: store these numbers in a list
Finally print out these numbers
2. There is a little monkey who picks a lot of peaches,
I ate half of all the peaches on the first day, I didn't feel full and ate another one
I ate the remaining half the next day and I didn’t feel full and ate another one
and so on...
By day 10, only one was left
ask: How many peaches were picked on the first day?
3. print the nine-nine multiplication table:
1x1=1
1x2=2 2x2=4
1x3=3 2x3=6 3x3=9
....
......................9x9=81
4. Enter as many student names as you want,age, grades,Information for each student
Store it in a dictionary, then put it in a list.
Information for each student needs to be entered manually:
like:
Please type in your name: tarena
Please enter age: 15
Please enter grade: 99
Please type in your name: china
Please enter age: 70
Please enter grade: 98
Please type in your name: <Enter> end input
The internal storage format is as follows:
infos = [{'name':'tarena', 'age':15, 'score':99},
{'name':'china', 'age':70, 'score':98}]
1. print the list above
2. Print student information in the form below
+---------------+-----------+----------+
| Name | age | score |
+---------------+-----------+----------+
| tarena | 15 | 99 |
| china | 70 | 98 |
+---------------+-----------+----------+
day07 review
two container classes
tuple tuple
dictionary dict
tuple
Can be understood as an immutable list(sequence container)
How to create a literal value
() 20, (20,) 100,200,300 (1,2,3)
How to create a constructor:
tuple() , tuple(iterable object)
operations on tuples:
+ += * *=
< <= > >= == !=
in / not in operator
index/slice value(Assignment is not supported)
dictionary dict
Variable, can store any type of,unordered container
key-value pair(key-value)
Dictionary keys are immutable and non-repeatable
How to create a literal value
{} {1:"one"} {1:"one", 2:'two'}
derivation:
{key expression : value expression for variable in iterable object if...}
Constructor way:
dict() dict(iterable object) dict(keyword argument)
dict(iterable) dict(**kwargs)
operation:
variable = dictionary[key] # value
dictionary[key] = expression # Add/modify the value corresponding to the key
del statement to delete the key-value pair from the dictionary
del dictionary[key]
in , not in operator
method in dictionary
D.clear()
D.pop(key) remove
D.get()
D.copy
D.keys()
D.values()
D.items()
...
Day08 Notes:
1. Collection set
1. Collection set (create)
gather set
Collections are mutable containers
Data objects within a collection are unique(cannot be repeated many times)
Collections are unordered storage structures,The data in the collection is not sequential
The elements inside the collection must be immutable objects
Collections are iterable(Can use for statement traversal)
A collection is equivalent to a dictionary with only keys and no values(The key is the collection's data)
The constructor that creates the collection
set() Create an empty collection object(The ____ does not work{}to create an empty collection)
set(iterable) Use iterable objects to create new collection objects
Example:
s = set() # s bind empty collection set()
s = set(range(1, 5)) # s = {1, 2, 3, 4}
s = set("hello") # s = {'e', 'o', 'h', 'l'}
Note:
For non-empty collections {} bracket,Use commas for each element inside(,)separated
Literal way to create a non-empty collection
s = {1, 2, 3, 4}
s = set("ABCCBA")
s = set({1:"one", 3:"three", 8:"Eight"})
s = set([1, 3.14, "ABC"])
s = {True, None, "ABC", (1, 2, 3)}
s = {True, None, "ABC", [1, 2, 3]} # error
2. Operations on sets
set operations:
intersection & union| Complement- Symmetric complement^ Subset< superset>
1. & Generate the intersection of two sets
s1 = {1, 2, 3}
s2 = {2, 3, 4}
s3 = s1 & s2 # s3 = {2, 3}
2. | Generate the union of two sets
s1 = {1, 2, 3}
s2 = {2, 3, 4}
s3 = s1 | s2 # s3 = {1, 2, 3, 4}
3. - generate the complement of two sets
s1 = {1, 2, 3}
s2 = {2, 3, 4}
# Generates the set of all elements with attribute s1 but not in s2
s3 = s1 - s2 # s3 = {1}
s3 = s2 - s1 # s3 = {4}
4. ^ generate the symmetric complement of two sets
s1 = {1, 2, 3}
s2 = {2, 3, 4}
s3 = s1 ^ s2 # {1, 4}
5. < Determine if a set is a subset of another set
> Determine if a set is a superset of another set
s1 = {1, 2, 3}
s2 = {2, 3}
s2 < s1 # True
s1 > s2 # True
s3 = {3, 4, 5}
s1 > s3 # False
s1 < s3 # False
s1 == s3 # False
6. == != Determine whether the sets are the same or different
{1, 2, 3} != {3, 2, 1} # False
7. >= <=
8. in , not in operator
equivalent to a list in operator
s1 = {1, 2, 3}
3 in s1 # True
Advantages of sets and dictionaries:
in / not in Operators operate faster
Built-ins that can be used for collections(built-in)function:
len(x)
max(x)
min(x)
sum(x)
any(x)
all(x)
practise:
manager has: Cao Cao, Liu Bei, Sun Quan
technicians have: Cao Cao,Sun Quan,Zhang Fei,Guan Yu
use set:
1. Who is the manager and the technician??
2. is the manager,but anyone who is not a technician?
3. is a technician,but anyone who is not a manager?
4. Is Zhang Fei the manager??
5. Who is the person who holds the job?
6. How many managers and technicians are there in total?
3. Commonly used collection methods in python3
python3 Commonly used collection methods in:
Documentation see:
python_base_docs_html/set.html
Collections are iterable objects
4. Set comprehension
set comprehension
Collection comprehensions are expressions that create collections from iterable objects
grammar:
{ expression for variable in iterable object [if truth expression]}
Note:[] Represents the contents of which can be omitted
Example:
L = [1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 7]
s = {x ** 2 for x in L}
Nesting of set comprehensions is equivalent to nesting of list comprehensions
2. Fixed set frozenset
Fixed collection frozenset
Fixed collections are immutable,disordered,A collection with unique elements
effect:
Fixed collections can be used as dictionary keys,Can also be used as a set value
Fixed collection constructor frozenset
frozenset() Create an empty fixed collection
frozenset(iterable) Create a new fixed with an iterable object
gather
Example:
fz = frozenset()
fz = frozenset("hello")
fz = frozenset([1,2,3,4,3,4,5])
1. Operations on fixed sets
Operations on Fixed Sets: intersection & union | Complement - Symmetric complement ^ in / not operator < <= > >= == != (The above operator usage is equivalent to set usage in) Ways to fix a collection,Equivalent to all methods of collections, except methods that modify collections
3. Staged summary
Staged summary:
type of data
immutable data type
bool, int, float, complex, str, tuple
frozenset, bytes(byte string,learn later)
mutable data type
list, dict, set, bytearray(byte array,I'll talk about it later)
value:
None, False, True
operator:
+ - * / // % **
> >= < <= == !=
in / not in
is / is not
not and or
& | ^
+(Positive sign) -(negative)
[] # Indexing and Slicing
expression:
1
True
1 + 2 * 3
print("hello") # function call
L.pop(2) # Method calls are also expressions
sum([1, 2, 5, 10])
conditional expression: x if x > y else y
all derivations: list,dictionary,set comprehension(three)
statement:
expression statement(Expressions can form expression statements on a single line)
print("hello")
"this is a text"
assignment statement:
a = 100
a = b = c = 200
x, y, z = 1, 2, 3
del statement
if statement
while statement
for statement
break statement
continue statement
pass statement
built-in function:
len(x)
max(x)
min(x)
sum(x)
any(x)
all(x)
--------- Constructor -------
bool(x)
int(x)
float(x)
complex(x)
str(x)
list(x)
tuple(x)
dict(x)
set(x)
frozenset(x)
-------------------
abs(x)
round(x, y)
pow(x, y, z=None)
--------------------
bin(x)
oct(x)
hex(x)
chr(x)
ord(x)
--------------------
range(start, stop, step)
----Basic input and output functions--
input(x)
print(....)
--------------------
id(x) return memory address
type(x) return type
2.5 Python functions
4. function function
1.function function
what is a function
A function is a block of statements that can be executed repeatedly,Can be called and executed repeatedly
A function is the smallest unit of procedural programming
effect:
Used to encapsulate statement blocks,Improve code reusability
Define user-level functions
Improve code readability and maintainability
2.def statement:
grammar:
def Function name(parameter list):
statement block
effect:
create a function,pack statement blocks,bind with function name,used to call
illustrate:
1. The naming rules for function names are the same as for variable names(must be an identifier)
2. function name is a variable,it is used to bind functions
3. Functions have their own namespace,Can't access inside a function from outside the function
Department variables,Variables outside the function can be accessed inside the function,but not right
external variable assignment
4. Statement part cannot be empty.If it is empty, it needs to be filled in pass statement
5. If the function does not need to pass in parameters,The parameter list can be empty
3.function call:
grammar:
Function name(The actual call passes the parameters)
illustrate:
A function call is an expression
If there is no inside the function return statement,Return after the function has finished executing None
object reference
For example see:
def.py
mymax.py
practise:
1. write a function myadd, There are two parameters in the parameter list in this function
number x, y The function of this function is to print x + y the sum
def myadd(...):
...
myadd(100, 200) # 300
myadd("ABC", "123") # ABC123
2. write a function print_even,pass in a parameter n Represents a terminating integer
print 2 4 6 8 .... n all even numbers between(Include n)
The function is defined as follows:
def print_even(n):
.... # Do it yourself here
print_even(8)
# Print:
2
4
6
8
5.return statement
return statement
grammar:
return [expression]
Note: [] Represents the contents of which can be omitted
effect:
used in function,end the execution of the current function,return to the caller of the function
place,Also returns a reference to an object
illustrate:
1. return The expression following the statement can be omitted,equivalent after omission
At return None
2. There is no inside the function return statement,the function executes the last
return after statement None(It is equivalent to adding a line at the end return None
statement)
For example see:
return.py
practise:
1. write a function mymax, The implementation returns the maximum value of three numbers:
like:
def mymax(a, b, c):
...
print(mymax(100, 200, 300)) # 300
print(mymax("ABC", 'abc', '123')) # abc
2. write a function myadd()Implementation gives two numbers,returns the sum of these two numbers
like:
def myadd(x, y):
....
a = int(input("Please enter the first number: "))
b = int(input("Please enter a second number: "))
print("The sum of the two numbers you entered is:", myadd(x, y))
3. write a function input_number
def input_number():
.... # Do it yourself here
This function is used to get the integer input by the user loop,End input when negative number is entered
Return the numbers entered by the user as a list,Reuse built-in functions max,min,
sum Find the maximum value of the number entered by the user,min and sum,like:
L = input_number()
print("The maximum number is:", max(L))
print("The minimum number is:", min(L))
print("and yes:", sum(L))
practise:
1. Create two functions
def sum3(a, b, c):
# returns the sum of three numbers
....
def pow3(x):
# used to return the cube of x
...
Use the above two functions to calculate:
1. Calculate the cube of 1 + 2 cube + 3 sum of cubes
2. Calculate 1+2+3 the sum of the cube
which is: 1**3 + 2**3 + 3 ** 3 and (1+2+3)**3
2. Rewriting previous student information management procedures,Encapsulated as two functions:
def input_student():
# This function is used to return a list of all user entered student information
...
def output_studentn(L):
# This function prints student information in tabular form
...
The following is the call(The function and printing effect are the same as before):
infos = input_student()
print(infos)
output_studentn(infos)
3. write function,Calculate the sum of the following polynomials:
Sn = 1/(1*2) + 1/(2*3) + 1/(3*4) + ...
... + 1/(n*(n+1))
def Sn(n):
...
print(Sn(3)) # 0.75
print(Sn(1000)) # ???
day08 review
two container classes
gather set, Fixed collection frozenset
Creation of collections
set()
set(iterable object)
{1, 2, 3, 4}
set comprehension: {expression for variable list in iterable object if ...}
Creation of fixed collections
frozenset()
frozenset(iterable object)
Collection features:
disorder, not repeatable,can only store immutable objects
set operations:
& | - ^ < > <= >= == !=
in, not in, is, is not(Judging is id)
collection method:
S.add(x) Add to:
S.remove(x)
S.discard(x)
S.clear()
S.pop()
two sentences
def statement
create a function,Use function variables to bind functions,The purpose is to later
to repeat the call
return statement
grammar:
return expression
Day09 Notes:
1. Passing parameters of functions (passing data to functions)
function parameters(pass data to the function)
function parameters(Receive data from function call)
python function parameter passing
delivery method:
1. location parameter
1.1 serial parameter
2. keyword argument
2.1 dictionary keyword argument
1. Location parameter
location parameter:
actual parameters(Arguments) The correspondence and formal parameters of(formal parameter)The corresponding relationship is
Corresponding by location.
For example see:
position_give_args.py
illustrate:
Arguments and formal parameters are passed and matched by position
The number of actual parameters must be the same as the number of formal parameters
2. Sequence parameter transfer
serial parameter:
Sequence parameter passing refers to the process of calling a function,use*(Asterisk) After disassembling the sequence
The way of passing parameters by position
illustrate:
When passing parameters in sequence,The position of the sequence disassembly will correspond to the formal parameters one-to-one
For example see:
sequence_give_args.py
3. Keyword parameters
keyword argument:
The keyword parameter refers to the time when the parameter is passed,Assign a value to a parameter by its name
Arguments and formal parameters are matched by name
illustrate:
Can not match by location
For example see:
keywords_give_args.py
4. Dictionary keyword parameters
dictionary keyword argument:
means that the argument is a dictionary,use the dictionary** After dismantling, pass keyword parameter transmission
delivery method
illustrate:
The key name and parameter name of the dictionary must be the same
The key name of the dictionary must be a string that conforms to the naming rules for identifiers
The key name of the dictionary must exist in the formal parameter
For example see:
dict_keyword_give_args.py
5. Comprehensive parameter transfer of functions
Synthesis of function parameters:
1. The way of passing parameters of a function is to ensure that the formal parameters can uniquely match the corresponding actual parameters.
can be combined in any
2. The positional parameters of the function should be passed before the keyword parameters.
Example:
def myfun(a, b, c):
pass
myfun(100, *[200, 300])
myfun(100, *"BC")
myfun(*"AB", 300)
myfun(*[100], 200, *[300])
myfun(100, c=300,b=200)
myfun(a=100, 200, c=300) # Incorrect
myfun(100, **{'c':300, 'b':200})
myfun(100, **{'c':300}, b=200)
myfun(100, b=200, **{'c':300})
practise:
write a function minmax,Pass in three parameters,Returns the maximum and minimum of these three parameters
small value element,result requirements,form tuple minimum first,The maximum value is returned after
to the caller
like:
def minmax(a, b, c):
....
The result of the call is as follows:
t = minmax(300, 100, 200)
print(t) # (100, 300)
2. The default parameters of the function
function default arguments
grammar:
def Function name(parameter name 1=Default argument 1, parameter name 2=Default argument 2,
parameter name 3=Default argument 3, .....)
effect:
Let the caller of the function pass fewer parameters to call the function
For example see:
default_args.py
illustrate:
1. Default parameters must exist in order from right to left,If a parameter has a default
parameter, then all parameters to the right of it must have default parameters
2. The default parameter can have 0,1 one or more,even all have default parameters
like:
def fn(a, b=10, c): # mistake
pass
def fn(a=0, b=None, c=False): # it's right
pass
practise:
write a function,myadd,This function can pass two,three or four arguments
The function of this function is to calculate the sum of all actual parameters
like:
def myadd(...):
....
print(myadd(10, 20)) # 30
print(myadd(100, 200, 300)) # 600
print(myadd(1, 2, 3, 4)) # 10
1. The passing of variable and immutable arguments of functions
Passing of variadic and immutable arguments to functions
For example see:
variable_args.py
variable_args2.py
illustrate:
When a mutable object is passed into a function via a function argument,inside the function
Mutable objects can be manipulated through local variables(list,dictionary,gather...)
interview questions:
What is the result of trying the following program, why?
L = [1, 2]
def fn(a, lst=[]):
lst.append(a)
print(lst)
fn(3, L) # [1, 2, 3]
fn(4, L) # [1, 2, 3, 4]
fn(5) # [5]
fn(6) # [5, 6]
fn(7) # [5, 6, 7]
3. How the function parameters are defined
How function parameters are defined positional parameter Asterisk tuple parameter Named Keyword Parameters Double asterisk dictionary parameter
1. Positional parameters
positional parameter:
grammar:
def Function name(formal parameter variable 1, formal parameter 2, ....):
statement block
2. Asterisk tuple parameter
Asterisk tuple parameter
grammar:
def Function name(*tuple parameter name):
statement block
effect:
Collect redundant location parameters
illustrate:
Tuple parameter names are generally named as'args'
*A function can only have one tuple parameter
For example see:
star_tuple_args.py
practise:
write a program, mysum Arbitrary parameters can be passed in,
The function of this function is to return the sum of all arguments
def mysum(*args):
....
print(mysum(1,2,3,4)) # 10
print(mysum(1,2,3)) # 6
3. Named Keyword Parameters
Named Keyword Parameters
grammar
def Function name(*,named keyword parameter 1, named keyword parameter 2,..):
statement block
or
def Function name(*args,named keyword parameter 1, named keyword parameter 2,..):
statement block
effect:
Forces all named keyword parameters to pass keyword or dictionary
key parameter
For example see:
named_keywords_args.py
think:
print() How is the parameter list of a function defined?
practise:
known built-in functions max The binding document is:
max(...)
max(iterable)---> value
max(args1, arg2, *args) --> value
counterfeit max function, write a max function exactly the same mymax function
(Require: Internal keys are not allowed to be called max function)
like:
def mymax(...):
...
print(mymax([6, 8, 3, 5])) # 8
print(mymax(100, 200)) # 200
print(mymax(1, 3, 5, 9, 7)) # 9
print(mymax()) # report an error
4. Double asterisk dictionary parameter
Double asterisk dictionary parameter
grammar:
def Function name(**dictionary parameter name):
statement block
effect:
Collect redundant keyword arguments
illustrate:
Dictionary parameter names are generally named as'kwargs'
There is at most one dictionary parameter in a function
For example see:
dict_kwargs.py
5. Formal parameter description of the function
1.Formal parameter description of the function:
Positional parameters, default parameters, asterisk tuple parameters, double asterisk dictionary parameters can be mixed
combined use
2.The definition order of function parameters from left to right is:
positional parameter
Asterisk tuple parameter
Named Keyword Parameters
Double asterisk dictionary parameter
Example:
def fn(a, b, *args, c, **kwargs):
pass
fn(1, 2, 3, 4, c=30, d=40, e=50)
3.Variable-length arguments to functions:
There are two: Asterisk tuple parameter, double asterisk dictionary parameter
Arbitrary parameters can be received with variable length parameters
like:
def fn(*args, **kwargs):
print(args, kwargs)
4. Global and local variables
Global and local variables
1.local variable
1. Variables defined inside a function are called local variables(The formal parameters of the function are also
local variable)
2. Local variables can only be used inside functions
3. Local variables can only be created when the function is called, and will be created after the function is called.
automatic destruction
2.global variable
1. defined outside the function,Variables inside a module are called global variables
2. All functions can directly access global variables(But inside the function you can't
its direct assignment)
illustrate:
Assignment statements inside functions do not affect global variables
practise:
1. write a function get_chinese_char_count(s),of this function
function is given a string,Returns the number of Chinese characters in this string
like:
def get_chinese_char_count(s):
...
s = input("Please enter a Chinese-English mixed string:")
print('The number of Chinese you entered is',
get_chinese_char_count(s))
Note: Chinese characters are encoded at 0 x4E00-0x9FA5 between
2. write a function isprime(x) judge x Is it a prime number.if prime
return True,otherwise return False
like:
print(isprime(3)) # True
print(isprime(4)) # False
3. write a function prime_m2n(m, n) return from m start,arrive n Finish
list of all prime numbers in the range,and print the corresponding list (does not contain n)
like:
def prime_m2n(m, n):
...
L = prime_m2n(10, 20)
print(L) # [11, 13, 17, 19]
4. write a function primes(n) Returns all prime numbers in the specified range
(does not contain n)list of,print a list of these prime numbers, like:
def primes(n):
...
L = primes(10)
print(L) # [2, 3, 5, 7]
1) print prime numbers up to 100
2) print the sum of all prime numbers up to 200
5. write a myrange function,The parameter can be passed 1~3 indivual,actual meaning
and range The function rules are the same,This function returns the range function rule
list of
like:
L = myrange(4)
print(L) # [0, 1, 2, 3]
L = myrange(4, 6)
print(L) # [4, 5]
L = myrange(1, 10, 3)
print(L) # [1, 4, 7]
day09 review
pass parameters(Arguments), pass data to the function(Give)
formal parameter,Receive arguments from where the function was called(take)
Parameters:
location parameter
sequence parameter function name(*sequence)
keyword argument
Dictionary keyword parameter function name(**dictionary)
When passing parameters,Difference between mutable and immutable objects
Immutable objects are not modified inside functions
function parameters:
Default parameter:
def f1(a=1, b=2):
pass
f1()
f1(100)
f1(100, 200)
How the formal parameters of the function are defined
positional parameter
*tuple parameter
Named Keyword Parameters
** dictionary parameter
Global and local variables
Day10 Notes:
1.globals() function and locals function
globals() function and locals function
globals() Returns a dictionary of variables in the current global scope
locals() Returns a dictionary of variables in the current local scope
For example see:
globals_local.py
2. Function variables
function variable
function name is variable,It binds a function when the function is created
For example see:
function_variable.py
function_variable2.py
A function can act as an argument passing of another function
You can assign a function to another function,The parameter variable of another function will be
bind argument function
For example see:
func_give_func.py
func_give_func2.py
#Understand the following code and judge the result
def myinput(fn):
L = [1, 3, 9, 5, 7]
return fn(L)
print(myinput(max)) # 9
print(myinput(min)) # 1
print(myinput(sum)) # 25
#A function can act on the return value of another function
For example see:
return_function.py
practise:
Write an interpretation executor that calculates the formula
The following functions are known:
def myadd(x, y):
return x + y
def mysub(x, y):
return x - y
def mymul(x, y):
return x * y
...
have a function that returns a function
def get_func(s):
'''This function function is,Pass in a string with s bind,according to s of
The value is returned to the corresponding function above, like s == '+'or s=='add' return
myadd
'''
.... Implement this function yourself
The program in the main function is as follows:
def main():
while True:
s = input("Please enter the calculation formula: ") # 1 plus 2
L = s.split() # L = ['1', 'Add', '2']
a = int(L[0])
b = int(L[2])
fn = get_func(L[1])
print("turn out:", fn(a, b)) # The result is: 3
main() # call the main function
3. Nested definitions of functions
Nested definitions of functions A function nested definition refers to a function that uses def statement to create other functions For example see: function_embed_define.py
4. The scope of python
1.python scope of
The scope is also called the namespace, which is the namespace of the variable to find when accessing the variable
2.python The four scopes in LEGB see table below:
For example see: namespace.py
| scope | English explanation | English abbreviations |
|---|---|---|
| local scope | Local(function) | L |
| outer nested function scope | Enclosing Fucntion local | E |
| The scope of the module (file) where the function definition is located | Global(module) | G |
| Scope of Python's built-in modules | Builtin(python) |
Lookup rules for variable names
L ---> E ---> G ----> B
Note:
by default,variable name assignment creates or changes the current scope
Binding relationship of internal variables
1.global statement
global statement
effect:
1. tell the interpreter,global one or more variables declared by the statement,This
Some variables are scoped at the module level,also known as global variable
2. global declaration(global) Map the variables of the assignment statement to the module text
Scope inside the file
grammar:
global variable name 1, variable name 2, ....
For example see:
global.py
illustrate:
1. If a global variable is to be assigned inside a function,must be declared globally
(Otherwise it will be considered a local variable)
2. Global variables can be accessed directly without declaration inside the function(value)
3. cannot create local variables first,reuse global declared as a global variable,this
this practice is against the rules
4. global The variable name in the variable list cannot appear in the formal parameter column of the function
Inside and outside
2.nonlocal statement
nonlocal statement
effect:
tell the interpreter, nonlocal The declared variable is not a local variable,neither
global variable,but a variable inside the outer nested function
grammar:
nonlocal variable name 1, variable name 2, ....
For example see:
nonlocal.py
illustrate:
1. nonlocal Statements can only be used inside nested functions
2. right nonlocal Assigning a variable will scope the outer nested function
operate on variables within
3. When there are two or more levels of function nesting,access nonlocal variable
Only operate on the nearest layer of variables
4. nonlocal The variable name in the variable list of the statement cannot appear here
in the parameter list of the function
practise:
Log a function with global variables hello the number of times it was called
Part of the code is as follows:
count = 0
def hello(name):
print("Hello", name)
... # Do it yourself here
hello("Xiao Zhang")
hello("Xiao Li)
print("hello function is called", count, "Second-rate") # 2
def The purpose of the statement is to create a function
5.lambda expressions (aka anonymous functions)
lambda expression(aka anonymous function)
effect:
Create an anonymous function object
same def similar,but don't provide the function name
grammar:
lambda [function parameter list]: expression
For example see:
lambda.py
illustrate:
1. lambda A function created by an expression can only contain one expression
2. lambda simpler than functions,and can be created and destroyed at any time,beneficial to
Reduce program coupling
practise:
1. write a lambda expression
fx = lambda n: .....
the function judgment created by this expression n the square of this number+1 Is it divisible by 5,
return if divisible True,otherwise return False
print(fx(3)) # True
print(fx(4)) # False
2. write a lambda expressions to create functions,This function returns two parameters
maximum number
def mymax(x, y):
....
mymax = lambda .....
print(mymax(100, 200)) # 200
3. See what the following program is doing?what's the result ?
def fx(f, x, y):
print(f(x, y))
fx((lambda a, b: a + b), 100, 200)
fx((lambda x, y: x**y), 3, 4)
6. The eval function and the exec() function
eval function and exec() function
eval(source, global=None, local=None), put one
string source Executed as an expression,return expression
result after row
exec(source, global=None, local=None) put one
string source execute as a program
For example see:
eval.py
exec.py
eval2.py
practise:
1. give a number n,write a function mysum to calculate
1 + 2 + 3 + .... + n the sum
require a function to do
like:
print(mysum(100)) # 5050
2. give a number n,write a function myfac to calculate n!(n factorial of)
n! = 1 * 2 * 3 * ... * n
print(myfac(5)) # 120
3. give a number n,write a function:
1 + 2**2 + 3**3 + .... + n**n the sum
4. Realization of student information management program with interface
The interface is as follows:
+----------------------+
| 1) Add student information |
| 2) View Student Information |
| 3) Delete student information |
| 4) Modify student grades |
| q) quit |
+----------------------+
please choose:1
Please enter student name: xiaozhang
Please enter student age: 20
Require each function to write a function corresponding to it(Reuse previous student information
hypervisor)
day10 review
local variable global variable
locals() globals()
def fa(a, b):
pass
A function can be passed as a parameter to another function
def fx(fn):
pass
fx(max) # pass in a function
A function can be the return value of another function
def fx():
return max
m = fx() # This function call returns a max function
def fy():
def hello():
print("hello")
return hello
h = fy()
h() # this
function nested definition
python four scopes:
local scope
outer nested function scope
global scope
Scope of built-in modules
global statement
nonlocal statement
def statement creation function
lambda expression
myadd = lambda x, y: x + y
eval(s) function
... expression ...
exec(s) function
... statement(program) ...
Day11 Notes:
2.6 Functional programming in Python
1. Functional programming
1.functional programming
Functional programming is the use of a series of functions to solve a problem
benefit:
1． Use each function to complete small functions, and any combination of a series of functions can complete large problems
2． Functions only take input and produce input, without any internal state that can affect output
2.reentrancy of functions
If the input parameters of a function are certain, the function that returns a certain result is called a reentrant function
Example:
# Reentrant function, the incoming parameters must be. the result must be
def myadd(x, y):
return x + y
# Non-reentrant functions:
y = 200
def myadd2(x):
return x + y
print(myadd2(10)) # 210
y = 300
print(myadd2(10)) # 310
3.Functional programming requirements:
def It is best not to create functions that access variables outside the local scope, so as to ensure the uniqueness of the returned results(reentrancy)
2. High Order Function
Higher order functions High Order Function
What is a higher order function:
A higher-order function is a function that satisfies one of the following conditions
1. A function accepts one or more functions passed in as parameters
2. function returns a function
python Built-in higher-order functions:
map, filter, sorted
see details:
python_base_docs_html/built-in function(builtins).html
1.map function
map function:
Format:
map(func, *iterables)
For example see:
map.py
practise:
1. use map function:
1**3 + 2**3 + 3 ** 3 + .... 9**3 the sum
2. use map function:
1**4 + 2**4 + 3 ** 4 + .... 20**4 the sum
hint: sum(map(.....))
2.filter function
filter function:
filter(function, iterable)
filter For example see:
filter.py
practise:
1. will 1 ～ ２０ for even numbers filter After generating the iterable object, put the number generated by the iterable object into the list L middle
2. write a function is_prime(x) judge x Is it a prime number
use filter function prints out: 20 ~ 30 all prime numbers between
3.sorted function
sorted function:
effect:
Sort the data of the original iterable object to generate a sorted list
Format:
sorted(iterable, key=None, reverse=False)
illustrate:
iterable iterable object
key The function is used to provide a value, which will be used as the basis for sorting
reverse The flag is used to set whether to sort in descending order
For example see:
sorted.py
practise:
names = ['Tom', 'Jerry', 'Spike', 'Tyke']
Sort by reverse order of strings:
'moT' yrreJ ekipS ekyT
result:
['Spike', 'Tyke', 'Tom', 'Jerry']
3. Recursive function recursion
1.recursive function recursion: A function calls itself directly or indirectly
recursive example:
# function calls itself directly
def f():
f() # call yourself
f()
# function calls itself indirectly
def fa():
fb()
def fb():
fa()
fa()
2.Recursion Description:
Recursion must control the number of recursive layers, and terminate recursion when certain conditions are met
Almost all recursion can be used while loop instead
3.Advantages and disadvantages of recursion:
advantage:
Recursion simplifies the problem, makes the thinking clearer and the code more concise
shortcoming:
Recursion is greatly affected by the system environment. When the recursion depth is too large, unpredictable results may be obtained.
4.two stages of recursion
recursion stage: Starting from the original problem, according to the recursive formula, recursion from the unknown to the past, and finally reach the termination condition of the recursion
regression phase: find the result according to the recursive termination condition,Reverse step by step into the recursive formula．return to the original problem
For example see: recursion.py
recursion_fac.py
practise:
write function mysum(n)summation recursively
def mysum(n):
# sum recursively
...
print(mysum(100)) # 5050
thinking questions:
Five friends are known to be together
The fifth friend is 2 years older than the fourth friend
The fourth friend is 2 years older than the third friend
The third friend is 2 years older than the second friend
The second friend is 2 years older than the first friend
First friend said it was 10 years old
4. Closure closure
Closure closure
1.what is a closure:
A closure is a function that refers to a variable outside this function
illustrate:
In essence, a closure is an object that binds together the inner nested function and the execution environment outside the function
2.A closure must satisfy three conditions:
1. There must be an inline function
2. Inline functions must reference variables in outer functions
3. The return value of the external function must be an inline function
For example see:
closure.py
# For the application of closures see:
closure2.py
practise:
1. Five friends are known to be together
The fifth friend is 2 years older than the fourth friend The fourth friend is 2 years older than the third friend The third friend is 2 years older than the second friend The second friend is 2 years older than the first friend First friend said it was 10 years old Write a program to print out the fifth friend with a third friend age
2. known list:
L = [[3, 5, 8], 10, [[13, 14], 15, 18], 20]
1) write a function print_list(lst) print out all elements
print(L) # print 3 5 8 10 13 14 ....
2) write a function sum_list(lst) Returns the sum of all elements in this list
print(sum_list(L)) # 86
Note:
type(x) The type that can return a variable
like:
>>> type(20) is int # True
>>> type([1, 2, 3]) is list # True
3. Rewriting previous student information management procedures
Request to add four features:
| 5) High grade by student-Low show student information |
| 6) Low grade by student-High display student information |
| 7) Highest by student age-Low show student information |
| 8) By student age-High display student information |
day11 review
Higher order functions
map, filter, sorted
recursion recursion
Closure closure
Day12 Notes
1. Decorators decorators (professional improvement)
1.decorator decorators(Professional Improvement)
A decorator is a function whose main function is to wrap another function or class(later)
The purpose of decoration is to not change the original function name(or class name) In the case of changing the behavior of the wrapped object
2.function decorator
A function decorator means that the decorator passes in a function and returns a function.
grammar:
def Decorator function name(parameter):
statement block
return function object
@Decorator function name<newline>
def Function name(parameter list):
statement block
For example see:
mydeco1.py
mydeco2.py
mydeco3.py
mydeco4.py
2. The docstring of the function
docstring of the function
The first string within a function that is not assigned to any variable is the function's docstring
grammar:
def Function name(parameter list):
'function docstring'
function statement block
Example:
def myfun(name, x):
'''This is the docstring of the function
name Indicates a person's name
x Indicates the amount of money
'''
pass
>>> help(myfun)
illustrate:
1. The docstring is usually used to describe the function and usage of this function
2. Type in interactive mode: help(Function name) function can be viewed'docstring'
3. A function's docstring is bound in the function's __doc__ attribute
functional __doc__ Attributes
docstrings for binding functions docstrings for binding functions
3. Complete syntax of function definition statement (def statement)
function definition statement(def statement) full syntax of:
[@decorator 1]
[@decorator 2]
[...]
def Function name([positional parameter], [*tuple parameter], [Named Keyword Parameters], [**dictionary parameter]):
'''docstring'''
statement block
Note: [] Represents its internal can be omitted
2.7 Modules
4. Module Module
module Module
what is a module:
A module is a collection of data,function,Program group composed of classes, etc.
A module is a file, and the module file name usually starts with.py end.
effect:
Let some related data, functions, classes, etc. be logically organized together to make the logical structure clearer
data in the module,Functions, classes, etc. can be provided to other modules or programs for use
Classification of modules:
Built-in modules(builtins) can be used directly in the parser
Standard library modules, Install python installed and ready to use
third-party modules(Usually open source),Need to install by yourself
User-written modules(Can be used as a third-party module for others)
5. Module import statement
1.import statement
module import statement
import statement
grammar:
import module name 1 [as Module new name 1], module name 2 [as Module new name 2], ....
Example:
import math # import math module
import sys, os
effect:
Import a module as a whole into the current module
usage:
module name.property name
or
module name.function property name(actual parameter)
like:
math.factorial(5)
dir(obj) The function returns a list of strings of all properties
help(obj) The function can view the relevant docstring of the module
practise:
1. Enter the radius of a circle and print the area of the circle
2. Enter the area of a circle and print the radius of the circle
(request math Function and data implementation within modules)
2.from import statement
from import statement
grammar:
from module name import module attribute name 1 [as property new name 1], module attribute name 2 [as property new name 2], ....
effect:
Import one or more properties of a module into the scope of the current module
Example:
from math import factorial as fac
from math import sin
from math import pi
print(fac(5)) # 120
3.from import * statement
from import * statement
grammar:
from module name import *
effect:
Import all properties of a module into the current module
Example:
from math import *
print(sin(pi/2))
print(factorial(5))
6.dir function
dir function:
dir([object]) returns a list of strings
illustrate:
If called with no arguments, returns a list of all variables in the current scope
If an object is given as a parameter, returns a list of all variables of this object
1) For a module, returns all properties of the module
2) For a class, return all variables of this class, and recurse all variables of the base class object
3) For other objects, return all class variables and base class variables
7. Built-in modules
built-in module
1.math module
module name math
see details:
python_base_docs_html/math module math.html
2. time module time
module name: time
see details:
python_base_docs_html/time module time.html
practise:
Write a program that inputs your date of birth,
1) Figure out how many days you've been born?
2) Figure out what day of the week you were born?
3.system module sys
Documentation see:
python_base_docs_html/system module sys.html
practise:
1. Please write a function fun Its function is to compute the sum of the following polynomials:
fn = 1 + 1/1! + 1/2! + 1/3! + 1/4! + .. + 1/n!
(of mathematical modules factorial accomplish)
beg n When equal to 100,fn the value of
take a look fn(100)what is the value of
2. Write a program to format an electronic clock:
HH:MM:SS format display time
request to change every second
3 write function f(n)find the sum of the next polynomial
fn = 1/1 - 1/3 + 1/5 - 1/7 + 1/9 .... 1/(2*n-1)the sum
beg n When the value is 1000000,
1) Print f(1000000) the value of
2) Print f(1000000) * 4 value to see what
day12 review
decorator
decorator function:
def decorated function name(fn):
...
return function
like:
def mydeco(fn):
return fn
@mydeco
def fun():
print("fun function is called")
fun = mydeco(fun)
Example:
def mydeco(fn):
def fx(a, b):
print("++++++")
fn(a, b)
print('------')
return fx
@mydeco
def fun(x, y):
pass
fun(100, 200)
function name and function call
def fun():
pass
print(fun) # print function bound by fun
print(fun()) # Call the function bound by fun and print the return result of the function
docstring of the function
def fx():
'''docstring'''
used for help() helper function
function object __doc__property binding docstring
module concept
A module is a collection of data,function,Program group composed of classes, etc.
import import
import statement:
import statement
import math, sys, time
from import statement
from math import sin,cos, pi
from import * statement
from math import *
dir() function
help() function
Use of modules:
math module
time module
sys module
Day13 Notes
1. Customize the module and import
1.custom module and import
Require:
Module filename suffix must start with .py end
Module filenames must be valid identifiers
Avoid name conflicts with builtin module names
Import method:
import statement
from import statement
from import * statement
For example see:
mymod.py
2.import The path order in which the statement looks for module files
import module name # where to find this "modulename.py"
1. Search for built-in modules
2. The path to search for when the program is running(current path)
3. sys.path provided path
sys.path is a list,The internal storage is the search path of the module
>>> import sys
>>> print(sys.path)
3.Install third-party modules or packages
pip3 install module name
Let import Statement can find its own module
1. Put your own modules in sys.path in a folder in
2. Revise sys.path list,A string to add a folder inside
(Note:This method only works for the current program)
like:
import sys
sys.path.append('/home/tarena')
For example see:
test_mymod2.py
2. Modular programming advantages
Advantages of modular programming:
1. Conducive to multi-person cooperative development
2. Make the code more maintainable
3. Improve code reuse
4. Helps to resolve variable name conflicts(Scope of global variables within modules
global in the module)
3. Import the module
1.module loading process
when the module is imported,All statements within the module are executed
If a module has been imported,Then the statements in the module will not be re-executed when importing again
2.The process by which modules are imported and executed
1. First search the relevant path to find the module name.py
2. Determine if there is a corresponding module for this module pyc document.if.pyc file ratio.py
New files are loaded directly.pyc document
3. if.pyc file ratio.py old file,use the module name.py generate .pyc
document,and load and execute
3.compilation of modules
compile explain execution
mymod.py -----> mymod.pyc --------> python3
4. Properties of the module
module properties
__doc__ Attributes
docstring for binding modules
The module's docstring is used for help(module) function to provide help information
For example see:
mymod2.py
__file__Attributes
file pathname to use for binding modules
__name__Attributes
__name__The attribute is used to record the name of the module itself
effect:
1. record module name
2. Used to determine whether the main module
illustrate:
When the module is the main module(That is, the first module to run)Runtime,
__name__property binding '__main__'
When this module is not the main module,__name__property binding module name
like:
mymod.py The module name is 'mymod'
5. The __all__ list of modules
modular__all__list
effect:
when used from xxx import *statement import,import only__all__
properties in the list
illustrate:
__all__A list is a list of strings used to store exportable properties
For example see:
mymod3.py
Module's hidden properties
in the module'_' properties at the beginning,Using from xxx import * guide
time will not be imported,These properties are often called hidden properties
For example see:
mymod4.py
6. Random module random
random module random
effect:
Blocks for simulating or generating random outputs
Documentation see:
python_base_docs_html/random module random.py
practise:
use random module,Randomly generate a 6-digit numeric password for yourself
442260
number guessing game:
Let the program randomly generate an integer(0~100)between,with variables x bind
Let the user loop through the input integers with y bind,print the guessing result
if y > x prompt the user"you guessed it"
if y < x prompt the user"you guessed small"
if y equal x request the user"congratulations you guessed it right",then exit
loop input,and print the number of times the user guessed the number
7. Package (module package) package
Bag(module pack) package
A package is a method of grouping modules into folders
effect:
Classify a series of modules,Helps prevent naming conflicts
One or some modules can be loaded when needed,instead of all modules
Example:
mypack/
__init__.py
menu.py
games/
__init__.py
contra.py
supermario.py
tanks.py
office/
__init__.py
excel.py
word.py
8. Package import
package import Import rules for the same module import Package names [as package alias] import Package names.module name [as Module new name] import Package names.subpackage name.module name [as Module new name] from Package names import module name [as Module new name] from Package names.subpackage name import module name [as Module new name] from Package names.subpackage name.module name import property name [as property new name] from Package names import * from Package names.module name import *
1. The init.py file and the __all__ list in the file
1.__init__.py document
__init__.py is a file that must exist in a regular package
__init__.py will be called automatically when the package is loaded
effect:
Write the contents of this package
Fill in the package's docstring inside the package
exist__init__.py The file can load some other dependencies of this package.
it module
2.__init__.py inside __all__list
effect:
Used to record which packages or modules in this package need to be imported
when used from Bag import *statement when importing a module,find only__all__
All modules or subpackages in
illustrate:
__all__list only from xxx import * kick in
For example see:
mypack/games/__init__.py
import The order in which the statement searches paths for packages: 1. The path to search for when the program is running(current working directory) 2. sys.path provided path
2. Relative import of packages
Relative imports of packages
The relative import of the package refers to the mutual import of the modules within the package
grammar:
from relative path package or module import property or module name
or
from relative path package or module import *
relative path:
exist from import statement and from imoprt *can be used in the sentence
use relative path
. represents the current directory
.. Represents the upper level directory
... Represents the upper-level directory
.... and so on
Note: Relative imports cannot go outside the package
For example see:
mypack/games/contra.py
practise:
1. Simulate Doudizhu licensing,54 cards in total
Spades('\u2660'), plum bossom('\u2663'), Hearts('\u2666')
square('\u2665')
A2-10JQK
king,little king
three,Each player is dealt 17 cards,Three cards left
Enter Enter,Print the 17 cards of the 1st person
Enter Enter,Print the 2nd person's 17 cards
Enter Enter,Print the 3rd person's 17 cards
Enter Enter,Show three hole cards
2. Modify the original student information management program,Split the program into modules:
Require:
1. main event loop while statement in main.py middle
2. show_menu function in menu.py middle
3. Functions related to student operations are placed in student_info.py middle
3. Print the Yanghui triangle(Only 6 layers are printed, thinking questions,talk tomorrow or the day after)
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
day13 review
custom module
identifier.py cannot be 123.py
imported statement:
import statement
from import statement
from import * statement
Path to search for modules:
1. Indexing built-in modules
2. current runtime path
3. search sys.path the path provided in
mymod.py ---> mymod.pyc ----> python3
Preset properties of modules
__doc__Attributes
__file__Attributes
__name__Attributes
main module '__main__'
Non-main module binding 'module name'
__all__list
The effect is limited to from import *when importing,import only__all__list
properties within
Module's hidden properties
_Properties starting with an underscore are in from import *will not be imported when imported
random module
name: random
function:
random.random()
random.randint()
random.randrange(...)
random.sample()
random.choice()
....
Bag package
package import:
import
from import
from import *
Example:
import Package names.xxx.yyy.zzz
from Package names.xxx.yyy.zzz import aaa
from Package names.xxx.yyy.zzz import *
__init__.py
effect:
Contents of the package:
function,data,docstring
__init__.py inner __all__list
Tell from import * What the statement imports
__all__ = ['contra', 'tanks']
Relative imports of packages
Can only be used in two statements:
from relative path import statement
from relative path import *statement
relative path:
.
..
...
Day14 Notes
1. exception exception (basic)
abnormal exception (Base) what is wrong Errors are problems that cause the program to not execute properly due to logic or syntax, etc. Features unpredictable what is an exception An exception is a state identified when a program fails.when lead-up occurs,program no longer execute down,And go to the place where this function is called to handle this error and return to positive normal state effect: used as a signal,Notify the upper-layer caller that there is an error that needs to be handled The program has two states: normal status/abnormal state
2.try statement
try Two syntaxes of the statement
try-except statement
try-finally statement
try-except syntax of the statement
try:
Statements that may trigger exceptions
except error type 1 [as variable 1]:
exception handling statement 1
except error type 2 [as variable 2]:
exception handling statement 2
except (error type 3, error type 4) [as variable 3]:
Exception Handling Statement 3
...
except:
exception handling statement other
else:
Statement where exception did not occur
finally:
final statement
2.effect:
try to catch errors,Get notified of exceptions,Convert the program from an abnormal state to a normal state and
continue
illustrate:
as clause is a variable used to bind the error object,can be omitted
except clause can have one or more,but at least one
else Clause can have at most one.can also be omitted
finally Clause can have at most one.can also be omitted
For example see:
try_except.py
practise:
write a function get_score() to get grades entered by students
information(0-100)the integer,If the input is abnormal,then this function returns 0,
Otherwise return the grade entered by the user
def get_score():
.... # Implement it yourself here (the try statement can be added inside the function)
score = get_score()
print("The student's grade is:", score)
python3 All error types in:
Documentation see:
python_base_docs_html/python all exception types.html
3.try-finally statement
try-finally statement
grammar
try:
Statements that may trigger exceptions
finally:
final statement
illustrate:
finally clause cannot be omitted
must not exist except clause
effect:
usually used try-finally statement to do the things that must be handled when the exception is triggered
whether the exception occurs or not,finally clause will be executed
Note:
try-finally Statements do not change the program(normal/abnormal)state
Example:
What is the following statement doing?:
def get_number():
s = input("Please enter an integer:") or '0'
i = int(s)
return i
print(get_number())
Rewrite the above program,make your own rules,Keep the program from crashing
after rewriting:
def get_number():
s = input("Please enter an integer:")
try:
i = int(s)
except:
i = 0
return i
4.raise statement
raise statement
effect:
trigger an error,Put the program into an abnormal state
Send error notification to caller
grammar:
raise exception type
or
raise exception object
or
raise # Retrigger the last exception
Example:
raise ValueError #
raise ValueError("???????")
For example see:
raise.py
raise2.py
practise:
write a function get_age() Used to obtain a person's age information
This function specifies that the user can only enter 1~140 integer between,if the user
Enter other data to trigger directly ValueError type of error notification
like:
def get_age():
....
try:
age = get_age()
print("The age entered by the user is:", age)
except ValueError as err:
print('User input is not 1~140 integer between'
',Failed to get age')
5.assert statement (assertion statement)
assert statement(assert statement)
grammar:
assert truth expression, Bad data(usually a string)
effect:
When the truth expression is False Time,create one with bad data
AssertionError type of error,and enter an abnormal state
Usually used to deliberately make a mistake
Equivalent to:
if bool(truth expression) == False:
raise AssertionError(Bad data)
For example see:
assert.py
6. Statement summary in exception
Statement summary in exception:
try-except statement
for capture(take over)error notification,Convert abnormal state to normal state
try-finally statement
for execution in any state(normal/abnormal)statements that must be executed
raise statement
trigger error(Send error notification),Put the program into an abnormal state
assert statement
Trigger on condition AssertionError type of error notification
7. Iterator
1.iterator Iterator
what is an iterator
Iterators are tools for accessing iterable objects
iterator means iter(obj) the object returned by the function(example)
Iterators can be used next(it) function to get the data of an iterable object
2.iterator function iter and next
iter(iterable) Get an iterator from an iterable,iterable
Must be an iterable object that provides an iterator
next(Iterator) from iterator iterator Get the next record in,like
If the next record cannot be fetched,then trigger StopIteration abnormal
illustrate:
Iterators can only take values forward,won't go back
use iter A function can return an iterator of an iterable object
Example:
L = [2, 3, 5, 7]
it = iter(L) # Get an iterator from the L object
print(next(it)) # 2
print(next(it)) # 3
print(next(it)) # 5
print(next(it)) # 7
print(next(it)) # StopIteration exception
# Use an iterator to access the integer sequence generator returned by the range() function
it = iter(range(1, 10, 3))
next(it) # 1
next(it) # 4
next(it) # 7
next(it) # StopIteration
For example see:
iterator.py
practise:
have a collection
s = {'Tang monk', 'Goku', 'Bajie', 'sand monk}
# Use the for statement to iterate over all elements as follows:
for x in s:
print(x)
else:
print("end of traversal")
# Please rewrite the above for statement into a while statement and iterator implementation
practise:
1. A ball falls from a height of 100 meters,The rebound height is the original height after each landing
half of,fall again,programming:
1) Figure out how high the ball bounces off the 10th behind
2) Calculate how many meters the ball travels after the 10th bounce
2. Decomposition prime factors.enter a positive integer,Decomposition prime factors
as input: 90 then print: 90=2*3*3*5
(A prime factor is the smallest prime number that is divisible by the original number(does not include 1))
3. Modify the original student information management program,Add exception handling statement,let the program
Executes logically in any case.
If entering grades,Age, etc. will not cause the program to crash
day14 review
abnormal
try-except statement catch exception
try-finally Statement Execute the statement that must be executed
raise statement that triggers an exception
raise exception type
raise exception type()
raise
assert Statement Assertion Statement
try:
Statements that may trigger exceptions
except exception type 1 as e:
...
except exception type 2:
...
except (exception type 3, exception type 4):
....
except:
....
else:
...
finally:
...
iterator
iterator
iter(iterable object) return iterator
next(iterator) value(when no value is triggered raise StopIteration)
iterative loop
for x in range(10):
...
Equivalent to
it = iter(range(10))
while True:
try:
x = next(it)
...
except StopIteration:
break
Day15 Notes:
1. Generator Generator
1.Builder Generator
what is a generator:
Generators are iterable objects that can provide data dynamically
Generators generate data while the program is running,Unlike container classes,it usually doesn't
Store a lot of data in memory,Instead, use now
benefit:
Does not take up computer memory
There are two types of generators:
generator function
generator expression
Definition of generator function
contain yield The function of the statement is a generator function,This function is called and will return
a generator object
yield translate to(produce or generate)
2.yield statement
grammar:
yield expression
illustrate:
yield can only be used for def in function,The purpose is to use this function as a generator
function usage
yield used to generate data,for iterators next(it) function usage
For example see:
yield.py
illustrate:
1. The invocation of the generator function will return a generator object,The generator object is
an iterable object
2. generator function return will trigger a StopIteration abnormal
(end of generation)
For a practical example of generator see:
myinteger.py
practise:
Write a generator function myevent(start, stop) used to generate from
start start,arrive stop Finish(does not contain stop) within the range
a series of even numbers
def myeven(start, stop):
.... # Do it yourself here
evens = list(myeven(10, 20))
print(evens) # [10, 12, 14, 16, 18]
for x in myeven(21, 30):
print(x) # print 22 24 26 28
2. Generator Expressions
generator expression
grammar:
(expression for variable in iterable object [if truth expression])
effect:
Create a new generator in a comprehensible form
illustrate:
if clause can be omitted
Generator expressions can also be nested like list comprehensions
Example:
gen = (x**2 for x in range(1, 5))
it = iter(gen) # get iterator
next(it) # 1
next(it) # 4
next(it) # 9
next(it) # 16
next(it) # StopIteration
practise:
known list:
L = [2, 3, 5, 7]
1) Write a generator function.Enable this function to provide data dynamically,number provided
Add 1 to the square of the number in the original list
2) Write a generator expression.enable this expression to provide data dynamically,supply
The data is the square of the numbers in the list plus 1
3) create a list,The data in this list is the square of the numbers in the original list plus 1
practise:
1.Try writing a generator myfilter function,This function is the same as the system built-in
filter Consistent function
2. Understand what is the output of the following functions?why?
1st program
L = [2, 3, 5, 7]
a = [x*10 for x in L]
it = iter(a)
print(next(it)) # ???
L[1] = 333
print(next(it)) # ???
2nd program
L = [2, 3, 5, 7]
a = (x*10 for x in L)
it = iter(a)
print(next(it)) # ???
L[1] = 333
print(next(it)) # ???
3. Iterative utility function
iterative utility function
The role of the iteration tool function is to generate an iterable object that meets the conditions
zip(iter1[,iter2[, ...]]) return a zip generator object
This object is used to generate a tuple,The data for this tuple comes from
each iterable in the parameter,The number of generated tuples starts from the smallest
An iterable object determines
enumerate(iterable, start=0) return a enumerate
generator object,This object generates type as(index,value pair) tuple of
Default index starts at zero,can also be used start specify
zip Example:
numbers = [10086, 10000, 10010, 95588]
names = ['China Mobile', 'China Telecom', 'China Unicom']
for t in zip(numbers, names):
print(t)
# result
# (10086, 'China Mobile')
# (10000, 'China Telecom')
# (10010, 'China Unicom')
for t in zip(numbers, names, range(1, 10000)):
print(t)
enumerate Example:
names = ['China Mobile', 'China Telecom', 'China Unicom']
# for t in zip(range(100000000), names):
# print(t)
for t in enumerate(names):
print(t)
# print (0, 'China Mobile') (1, 'China Telecom') (2, 'China Unicom')
for t in enumerate(names, 101):
print(t)
# print (101, 'China Mobile') (102, 'China Telecom') (103, 'China Unicom')
zip For an example of the principle of the function, see:
myzip.py
practise:
write a program,Read in any line of text,End input when a blank line is entered,
print the input result with line numbers
like:
please enter: hello<Enter>
please enter: abc<Enter>
please enter: tarena<Enter>
please enter: <Enter>
print as follows:
line 1: hello
line 2: abc
line 3: tarena
container list,string,tuple(sequence), byte string,byte array dictionary,gather,Fixed collection
4. Byte strings and byte arrays
1.Byte strings and byte arrays
1.byte string(byte sequence) bytes
Store data in bytes
A bytestring is an immutable sequence of bytes
illustrate:
byte is 0~255 integer between,Used to represent the value of a byte
1.A literal way of creating an empty byte string:
b''
b""
b''''''
b""""""
2.Creates a literal value of a non-empty byte string
b'ABCD'
b"ABC"
b'''aaaa'''
b"""BBBB"""
2.Byte string constructor bytes
bytes() generate an empty bytestring,Equivalent to b''
bytes(Integer iterable object) Initialize a byte string with an iterable object
bytes(integer n) generate n a byte string with a value of 0
bytes(string, encoding='utf-8') Convert to byte string
code to generate a byte string
Example:
B = bytes()
B = bytes(range(0x41, 0x61))
B = bytes([65, 66, 67, 68])
B = bytes(10)
B = bytes("Hello", 'utf-8')
B = bytes("Chinese", 'utf-8')
3.Operations on byte strings:
+ += * *=
< <= > >= == !=
in / not in
Indexing and Slicing
4.function: len(x), max(x), min(x), sum(x), any(x), all(x)
5.bytes and str difference:
bytes storage bytes(0~255 integer between)
str storage UNICODE character(0~0x10FFFF) character of
6.bytes and str conversion
coding(encode)
str --------------> bytes
b = s.encode(encoding='utf-8')
decoding(decode)
bytes ---------------> str
s = b.decode(encoding='utf-8')
Example:
s = "ABC Chinese"
b = s.encode('utf-8')
s2 = b.decode('utf-8')
print(s, b, s2)
2.byte array bytearray: mutable byte string
1.Byte array constructor bytearray
bytearray()
bytearray(Integer iterable object)
bytearray(integer n)
bytearray(string, encoding='utf-8')
2.operation:
same byte string
+ += * *=
Compare: < <= > >= == !=
in / not in
index/slice
(Byte arrays can be indexed and sliced for assignment,The same rules as indexing and cutting of lists
slice assignment rule)
3.bytearray Methods:Documentation see: python_base_docs_html/bytearray.html
practise:
1. Write a generator function myxrange([start,]stop[,step])
to generate a series of integers
Require myxrange function and range The function is exactly the same
(call not allowed range Functions and Lists)
written by myself myxrange,Combine generator expressions to find all within 100
some odd sum of squares
2. Write a generator function fibonacci, Before generating Fibonacci numbers n
number
1 1 2 3 5 8 ....
like:
def fibonacci(n):
...
yield ...
...
1) print the first 20 numbers:
for x in fibonacci(20):
print(x)
2) Print the sum of the first 40 Fibonacci numbers
print(sum(fibonacci(40)))
3. thinking questions:
How to enable the student management system to read the information in the file to load
data? (Preview file operations)
day15 review
Builder
Generate data dynamically
There are two types of generators:
generator function
generator expression
generator function:
def myxxxx(....):
...
yield statement
...
A call to a generator function just returns the generator
use next(it) to iterator(Builder) when you want data,The generator function will
implement
The generator function encountered during execution yield will be suspended(hang),will yield
The generated data is returned to next(it) function
def myxrange(...):
...
for x in myxrange(1, 10, 3):
print(x)
generator expression:
(x*2 for x in range(10))
[x*2 for x in range(10)]
zip(iterable, *args) function
enumerate(iterable, start=0) function (0, "ABC")
byte string bytes and byte array bytearray
byte byte
is a storage unit of 8 bits
byte string: literal value
b'' b"" b'''''' b""""""
b'ABC' b'123' b'hello'
Constructors for byte strings and byte arrays
bytes() bytearray()
bytes(iterable object) bytearray (iterable object)
bytes(integer n) bytearray(integer n)
bytes(string, coding'utf-8') bytearray(...)
operation:
+ += * *=
< > <= >= == !=
in / not in
Indexing and Slicing
sequence:
str, list, tuple, bytearray, bytes
len(x), max(x) ....
Day16 Notes:
1. File
1.document File
A file is the basic unit for storing data
Files are often used for long-term storage of data
The data in the file is stored sequentially in bytes
2.File operation process
1. open a file
2. read/write file
3. close file
Note: any operating system,The number of simultaneously open files for an application
maximum number limit
3.file open function
open(filename, mode='rt') for opening a file,return
the file stream object used to manipulate this file,If opening fails,
will trigger OSError error notification
4.Close method of file stream object
F.close() close file.Free up system resources
For example see:
file_open.py
Command to display file contents in hexadecimal:
$ xxd file name
python Read and write operations of Chinese text files:
Documentation see:
python_base_docs_html/document file.html
For an example of reading a text file see:
file_read_text1.py
practise:
write a file yourself"info.txt", Some text information is stored internally as follows:
Zhang San,20,100
Li Si,18,98
little king,22,95
Write a program to read these data out,and printed on the screen terminal in the following format
Zhang San is 20 years old,grade is: 100
Li Si is 18 years old,grade is: 98
Xiao Wang is 22 years old,grade is: 95
file stream object readlines For an example of the method see:
file_read_text2.py
read For an example of how to use the method, see:
file_read_text3.py
2. The text file mode of python3
python3 text file mode
pattern character: 't'
illustrate:
1. Read and write operations on text files require strings(str)read and write operations
2. Automatic encoding during reading and writing(encode) and decoding
(decode)operate
3. separated by row,exist python Internal unified use'\n'newline character
to separate
Line breaks for each operating system:
Linux newline: '\n'
Windows newline: '\r\n'
new Mac OS newline: '\n'
3. Write operation of text file
Writing a text file:
method:
F.write(x)
F.writelines(list)
pattern string:
'w'
'x'
'a'
See documentation for details: python_base_docs_html/document.html
For example see:
file_write_text.py
practise:
1. write a program,Enter the names of many people,age,grades in file
'infos.txt'middle
Define the file format yourself(Commas are recommended(,)to separate the information)
Check to see if the file format is what you want when you're done typing
(Working with text files)
L = input_student()
def save_to_file(L, filename='infos.txt')
..
save_to_file(L)
4. Binary file operations
binary file operations
binary mode characters: 'b'
The default file is stored in bytes(byte)data in units,ordinary people
artificial format
Reading and writing binary files requires strings(bytes) or bytes
array(bytearray)operate
For binary file read and write methods, you need to operate in bytes
F.read(n)
F.readline()
F.readlines()
F.write(byte string)
F.writelines(a list of byte strings)
For example see:
file_read_binary.py
For an example of writing a binary file, see:
file_write_binary.py
5.F.seek method
F.seek method
effect:
Set the read and write location of the file,Returns the new read and write location
Format:
F.seek(Offset, whence=relative position)
Offset
Greater than 0 means move to the end of the file
Less than 0 means move to the head of the file
relative position:
0 represents the offset from the beginning of the file
1 Represents the offset from the current read and write position
2. represents the offset from the end of the file
For example see:
seek.py
6. Standard input and output files
standard input and output files:
module name:
sys
sys.stdin standard input file(Default is keyboard)
sys.stdout standard output file(Default is screen terminal)
sys.stderr standard error output file(Default is screen terminal)
Note: Standard files do not need to be opened to use,No need to close manually
For example see:
stdout.py
7. Chinese character encoding
How many bytes do ten Chinese characters occupy?
Chinese character encoding(only two)
GB series:
GB18030(Two-byte or four-byte encoding, 27533 words)
GBK(two-byte encoding,20013 words)
GB2313(two-byte encoding,About 7,000 words)
(Windows Commonly used)
international standard:
UNICODE(UNCODE16/UNICODE32) <-> UTF-8
(Linux/Mac OS X/ IOS/ Android Commonly used)
UTF-8 middle:
English ASCII (0x0 - 0x7F) one byte
(0x80 - 0x3FF) two-byte
(0x400 - 0xFFFF) three bytes(Chinese in this area)
python encoded string:
'gb2312'
'gbk'
'gb18030'
'utf-8'
'ascii'
...
like:
s = "Hello"
print(s.encode('gbk'))
print(s.encode('utf-8'))
print(s.encode('ascii'))#Error, "hello" is not in ascii
1. Coding Comments
Coding Comments: in the source file,The following content written in the first or second line is an encoding comment # -*- coding:gbk -*- or # -*- coding:utf-8 -*-
practise:
1. Write a program to implement the function of copying files
Require:
1. Consider the problem of very large files
2. To be able to copy binary files(like:pictures etc.)
3. Consider closing the file
2.Rewrite the original student information management program,The following two functions are required to be added:
| 9) read data from file(si.txt) |
| 10) Save information to file(si.txt) |
day16 review
document:
There are two ways to read and write:
binary mode: 'b'
byte string/byte array
text file: 't'
string(Default is'utf-8'coding)
Two operating modes:
read file read(INPUT operate)
'r'
write file write(OUTPUT operate)
'w','x','a'
process:
1. open a file
2. read/write file
3. close file
open(file pathname, pattern string='rt') return file stream object
F.close()
F.read(n)
F.readline()
F.readlines()
F.write(byte string/string)
F.writelines(byte string/string list)
F.seek(Offset, relative position)
F.tell()
F.flush() clear the buffer
Chinese character encoding:
two:
UNCODE coding <--> UTF-8
'utf-8'
GB serial number
'gb2312'
'gbk'
'gb18030'
ASCII English code:
'ascii'
Coding Comments:
# -*- coding:utf-8 -*-
# -*- coding:gbk -*-
Day17 Notes:
2.8 Object-Oriented Programming in Python
1. Ojbect-Oriented Programming
1.Object-Oriented Programming Ojbect-Oriented Programming
Two programming ideas: procedural programming --> The smallest unit is: function function
object oriented programming --> The smallest unit is: kind class
2.what is an object: Object refers to an object or entity in reality
3.What is Object Orientation: treat everything as an object(example) Describe things in terms of relationships between various objects
4.What are the characteristics of the object:(1)Objects have many properties(noun,adjective)-- Name, age, gender, Hair color
(2)Objects have many behaviors(action,verb) -- study,Have a meal,sleep,kick the ball,Work
2. What is a class
1.what is a class
Objects with the same properties and behavior are grouped together,a class
Classes are tools for describing objects,Objects of this class can be created with classes(example)
signal:
car(kind) ----> BYD E6(Beijing A.88888) example
\
\--> BMW X5(Beijing B.00000) object(example)
dog(kind) ----> Little Beijing(Household registration number: 000001) object
\
\---> guide dog(Household registration number:00002) object
int(kind) -----> 100 object
\
\---> 200 object
2.class creation statement:
grammar:
class class name(inheritance list):
'''class docstring'''
instance method(functions within a class method)definition
class variable
class method(@classmethod)
static method(@staticmethod)
effect:
create a class
Classes are used to describe the behavior and properties of objects
A class is used to create one or more objects of this class(example)
illustrate:
class name must be an identifier
The class name is actually a variable,it binds a class
For example see:
class.py
3.class constructor
Format:
class name([parameter list])
effect:
Create an instance object of this class,And return the reference relationship of this instance object
For example see:
constructor.py
illustrate:
object(example)Class methods and instance methods can be called
object(example) Has its own scope and namespace,can be added to this instance
instance variable(Also called instance property)
4.instance method(instance method)
Define the format:
class class name(inheritance list):
def instance method name(self, parameter 1, parameter 2, ...):
'''docstring of the method'''
statement block
effect:
Used to describe the behavior of an object,make all objects of this type have the same
the behavior of
illustrate:
The essence of an instance method is a function,is a function defined in an inner class
Instance methods have at least one parameter,The first parameter binds the instance that calls this method
example,Commonly named as'self'
5.Instance method invocation syntax:
example.instance method name(call parameter)
or
class name.instance method name(example, call parameter)
For example see:
instance_method.py
6.instance properties attribute (Also called instance variable)
Each instance can use its own variables to record each object's own data,this
variable called instance variable
use syntax:
example.property name
assignment rule:
This property is created the first time a property is assigned a value
Assigning a value to a property again changes the binding relationship of this property
effect:
Record each object's own data
practise:
define a"people" kind
class Human:
def set_info(self, name, age,
address="unknown"):
... Do it yourself here
def show_info(self):
'''This information is displayed here'''
... Do it yourself here
s1 = Human()
s1.set_info('Xiao Zhang', 20, 'Dongcheng District, Beijing')
s2 = Human()
s2.set_info('Xiao Li', 18)
s1.show_info() # Xiao Zhang is 20 years old and lives in: ...
s1.show_info() # Xiao Li is 18 years old, home: unknown
7.delete attribute:
del statement
del object.instance variable name
del Statement summary:
1) delete variable del a,b,c
2) remove element from list del L[0], L[0:3]
3) delete key from dictionary del d['name']
4) delete attribute del obj.name
8.initialization method
effect:
Add properties to newly created objects
syntax format:
class class name(inheritance list):
def __init__(self [,parameter list])
statement block
Note:[]Represents the contents of which can be omitted
illustrate:
1. The name of the initialization method must be '__init__' immutable
2. The initialization method is called automatically after the constructor creates the instance,and will be
The example itself passes the first parameter self incoming'__init__' method
3. The arguments to the constructor will be passed through__init__method parameter list
into__init__method
4. Inside the initialization method if needed return return,must return None
For example see:
init_method.py
practise:
write a student class Student kind,This class is used to describe student information,student
information has: Name,age,score(Default is 0)
1) Add an initialization method to the class,Implements automatic settings when the object is created:
name, age, score Attributes
2) Add to set_score method,Ability to modify grade information for objects
3) Add to show_info method to print the information of the student object
like:
class Student:
def __init__(....):
....
def set_score(....):
...
def show_info(...)
...
L = []
L.append(Student('Xiao Zhang', 20, 100))
L.append(Student('Xiao Li', 18, 95))
L.append(Student('small money', 19))
L[-1].set_score(70)
for s in L:
s.show_info()
2. Destructor method
Destructor
Format:
class class name(inheritance list):
def __del__(self):
....
effect:
Release the resources occupied by this object before this object is destroyed
illustrate:
The destructor method is called automatically before the object is destroyed
python The language advises against doing anything on object destruction,because of the destruction
time is difficult to determine
For example see:
del_method.py
3. Preset instance properties
Preset instance properties
__dict__ Attributes
__dict__property binding a dictionary that stores this instance's own variables
Example:
class Dog:
pass
dog1 = Dog()
print(dog1.__dict__) # {}
dog1.color = "White"
print(dog1.__dict__) # {'color': "white"}
4.class attribute
__class__ Attributes
__class__ property binding the class that created this instance
effect:
The class that created this instance can be accessed with the help of this property
Example:
class Dog:
pass
dog1 = Dog()
print(dog1.__class__)
dog2 = dog1.__class__() # Dog()
5. Functions for instance objects
functions for instance objects:
isinstance(obj, class_or_tuple) return this object obj
is an object of a class,or an object of a class within some class.if
return if yes True,otherwise return False
type(obj) the type of the returned object
Example:
class Dog:
pass
dog1 = Dog()
isinstance(dog1, Dog) # True
isinstance([1,2,3], Dog) # False
isinstance([1, 2, 3], (int, str)) # False
isinstance([1, 2, 3], (int, str, list))#True
type(dog1) is Dog # True
practise:
there are two people:
the first person: Name:Zhang San, age:35 age
second person: Name:Li Si, age:15 age
Behavior:
1. teach others to learn teach
2. work to make money work
3. borrow money borrow
4. show your information show_info
matter:
Zhang San teaches Li Sixue python
Li Si teaches Zhang San learns the glory of the king
Zhang San earned 1,000 yuan at work
Li Si borrowed 200 yuan from Zhang San
35 The old Zhang San has 800 yuan,The skills it learns are: King of Glory
15 Year-old Li Si has 200 yuan,The skills it learns are: python
practise:
1. perfect number:
1 + 2 + 3 = 6 (6 is a perfect number)
1, 2,3 are all factors of 6(can be counted by a number x Divisible numbers y,but y for
x factor of)
1 x 6 = 6
2 x 3 = 6
Exactly means the sum of all factors except itself is equal to itself
ask for 4 - 5 perfect number
Answer:
6
28
496
...
2. The Student Information Management Program,dictionary for storing student information,replace with
use Student type object to store student information
day17 review
object oriented:
what is an object
what is a class
characteristics of objects:
Attributes
industry
kind class
Classes are used to describe objects, created objects(example)
instance method
class class name:
def instance method name(self, method parameter list):
statement block
call syntax:
object.instance method name(Arguments)
class name.instance method name(object, Arguments)
class within class:
class class name:
instance method(self, ...):
...
class variable
class method
static method
Constructor
class name(call arguments) Create an instance(object)
instance variable(instance properties)
record object data
v = object.property name # value
object.property name = v # Assignment (create or modify instance variables)
delete instance variable
del object．property name
initialization method:
def __init__(self, method parameters):
....
effect:
Create instance variables(instance properties)
Destructor:
def __del__(self):
...
Preset instance properties:
__dict__ bind instance variable(instance properties)dictionary
class Dog:
pass
dog1.color = "White" ＃ add instance variable
dog1.__dict__['kinds'] = "Beijing" # add instance variable
__class__ bind the class that created this instance
type(obj) return obj.__class__
type(obj) # The return type is equivalent to obj.__class__
isinstance(obj, class or tuple of classes)
obj.__class__ is kind
or
obj.__class__ in tuple
Day18 Notes:
2.9 Advanced Object-Oriented Programming in Python
1. Class
1.kind
define method:
class class name:
...
classes are objects,It is an object that can create instances
2.class variable
A class variable is an attribute of a class, this attribute belongs to the class, not an instance of this class
effect:
Commonly used to store common properties of objects created by this class
illustrate:
Class variables can be accessed directly through the class
Class variables can be accessed directly through an instance of the class(value)
Class variables can be accessed through objects of this class__class__property indirect access
For example see:
class_variable.py
Both instance methods and class methods are variables of the class(class variable)
2. Class docstring
class docstring:
The first string in the class that is not assigned to any variable is the class's document
string
A class's docstring is bound in the class's __doc__ attribute
Example:
class Dog:
'''Dog class docstring'''
>>> help(Dog)
>>> print(Dog.__doc__)
3. Class slot list
Category __slots__ list:
effect:
Instances created by restricting a class can only be created in fixed properties(instance variable)
Objects are not allowed to add instance properties other than this list
A program error occurred for the accessing user due to a mistyped attribute name
illustrate:
__slots__property is a list,The value of the list is a string
contain__slots__The instance object created by the class of the property does not have
__dict__Attributes,That is, this instance does not use a dictionary to store instance attributes
For example see:
slots.py
4. Class method @classmethod
class method @classmethod
Class methods are methods used to describe the behavior of a class,class method belongs to class,Does not belong
Objects created by this class
illustrate:
1. Class methods need to use@classmethod Decorator Definition
2. A class method has at least one parameter,The first parameter is used for binding
kind,Convention is written as'cls'
3. Both a class and an instance of that class can call class methods
4. Class methods cannot access instance properties of objects created by this class
For example see:
classmethod.py
5. Static method @staticmethod
static method @staticmethod
A static method is a function defined inside a class,The scope of this function is inside the class
illustrate:
1. Static methods need to be used@staticmethod Decorator Definition
2. A static method is the same as a normal function definition,No need to pass in self
and cls parameter
3. Static methods can only be called with the class or an instance of the class
4. Static methods cannot access class and instance variables
For example see:
staticmethod.py
6. Function, static method, class method, instance method
function,static method, class method, instance method:
commonality:
statement block,implement the corresponding function
practise:
1. Use a class to describe a student's information(You can also rewrite the previous
Student kind)
2. Student information has:
Name,age,score
3. Store these student objects in a list,can be added arbitrarily,and
Delete student information
1) print out the number of students
2) Print out the grade point average for all students
3) Print out the average age of all students
(It is recommended to use a class variable to record a list of student information)
7. Inheritance and derived
1.inherit inheritnce and derived derived
what is inheritance／Derive
Derivation is to derive a new class from an existing class
Inheritance means that objects in a derived new class will have the properties of the original class
sex and behavior
effect:
Using inheritance derivation mechanism, you can add some common functions to the base class．
Implement code sharing
Change the function of the original class without changing the base class code
noun:
base class(base class)/superclass(super class)/father
kind(father class)
Derived class(derived class) / Subclass(child class)
8. Single inheritance and the __base__ attribute of the class
2.single inheritance:
grammar:
class class name(base class name):
statement block
illustrate:
Single inheritance refers to a class that derives from a derived class from a base class
For example see:
inherit.pyinherit.py
Inheritance Notes:
python3 Any class in which directly or indirectly inherits from object kind
object Class is the superclass of all classes
3.Category__base__Attributes
__base__ Attribute is used to record the base class of this class
python For the inheritance relationship of built-in classes, see:
>>> help(__builtins__)
9. Overriding overridde
cover overridde
Overriding refers to in the class with inheritance relationship．The subclass implements the same as the base class
The method of the same name, when the instance of the subclass calls the method, the actual call
is the overridden version of the subclass, a phenomenon called overriding
effect:
Implement a method with the same name as the parent class but with different functions
For example see:
override.py
question:
when an overwrite occurs, How to call the overridden method of the parent class?
10.super function
1.super function
super(cls, obj) Returns an instance of the bound superclass(Require obj must
Yes cls class or cls object of subclass)
super() Returns an instance of the bound superclass, equivalent to:
super(__class__, The first parameter of an instance method),
must be used within a method call
effect:
with the help of super() The returned instance indirectly invokes the overridden method of the parent class
For example see:
super.py
2.super Applications
Explicitly call the initializer method of the base class
When the subclass implements__init__method, base class__init__method
will not be called automatically.If you need to call, you need to use super explicit
transfer.
For example see:
super_init.py
practise:
1. write a class Bicycle bicycle,Have run method,when called
Show mileage km
class Bicycle:
def run(self, km):
print("bike ride", km, 'kilometer')
write another EBicycle Electric bicycles,exist Bicycle The basics
Added battery power on volume Attributes,There are two methods:
fill_charge(vol) to charge vol for electricity
run(km) method,10 per ride km 1 degree of power consumption,Simultaneously display
Display the current battery,Called when the battery runs out Bicycle of run method
(ride with pedals)
class EBicycle:
....
b = EBicycle(5) The newly bought electric car has 5 kWh of electricity
b.run(10) 10 electric rides km inside,4 kWh left
b.run(100) 40 electric rides km inside,0 kWh left,with pedals
60 rides km
b.fill_charge(10) Electric bike charging 10 degrees
b.run(50) 50 electric rides km inside,5 kWh left
day18 review
kind -> object (example)
class object(instance)
object:
real variable(instance properties)
List method
kind:
class variable(class attribute)
class method(@classmethod)
@classmethod
def myclassmethod(cls, ....):
....
static method(functions within a class)
Preset class properties(class variable)
__docs__ binding docstring
__base__ Bind the base class of the current class(father)
__slots__list
Restrict a class to only have fixed instance variables(instance properties)
inherit / Derive
single inheritance
class class name(only one parent class):
pass
cover:
Inheritance-related classes,A subclass implements a method with the same name as the superclass,subclass call
The method actually calls the overridden version of the subclass
once covered,There is no way for subclass objects to directly call the overridden method of the parent class
super(kind, object)
super() # can only be called from within a method
use super Explicitly call the parent class __init__ initialization method
super().__init__(Pass arguments to the initial method of the parent class)
Day19 Notes
1. Functions for classes
functions for classes:
issubclass(cls, class_or_tuple) determine whether a class is
Does it inherit from a class class or some class tuple middle
a class,return if yes True,otherwise return False
Example:
class A:
pass
class B(A):
pass
class C(B):
pass
issubclass(C, B) # True
issubclass(bool, int) # True
issubclass(str, (A, B, int, float)) # False
issubclass(str, (A, B, int, object)) # True
Features of Object-Oriented Programming Languages: inherit package polymorphism
2. Package
package Encapsulation refers to hiding the implementation details of a class,Let users not care about these details The purpose of encapsulation is to allow the user to pass as few methods as possible(or attribute)Hold target
3. Private properties and methods
private properties and methods python double underscore in class__beginning,identifiers that do not end with a double underscore is a private member,Private members can only be accessed using the methods of the class and Revise For example see: enclosure.py
4. polymorphic
1.polymorphism polymorphic
literal meaning: 'multiple states'
2.The state of programming languages:
static(compile-time state) # C/C++
dynamic(runtime state) # C++/Java
3.Polymorphism originally refers to classes with inheritance relationship,Call a method of the base class object,actual energy
The phenomenon of calling to a subclass to override a method is called polymorphism
illustrate:
python All objects are only'runtime state(dynamic)',No
C++compile-time state in the language(static)
For example see:
poly.py
5. multiple inheritance
multiple inheritance multiple inheritance
Multiple inheritance is when a subclass inherits from two or more base classes
syntax for multiple inheritance:
class class name(base class name 1, base class name 2, ...):
statement
illustrate:
1. A subclass inherits from multiple parent classes at the same time,The method in the parent class can be the same as
inherited when
2. If two parent classes have methods with the same name,And in the subclass there is no override
cover this method,Call result is difficult to determine
For example see:
multi_inherit.py
Multiple inheritance problem(defect)
identifier(namespace) conflicting issues
Use multiple inheritance with caution
For example see:
multi_inherit2.py
multiple inheritance MRO(Method Resolution Order) question
MRO --> solution(find)order
Category __mro__Attributes
The search order used to record the methods of the class
For example see:
mro.py
6. Use of object to string function
Use of object to string function
repr(obj) return an attachment python a string of grammar rules,
usually:
eval(repr(obj)) == obj
str(obj) Returns a string with the given object(this character
Strings are usually read by humans)
For example see:
repr_str.py
illustrate:
The above two functions must return a string
7. Function rewriting
1.function rewrite
Function overriding refers to adding the corresponding method in the custom class,let's customize
Instances of the class can be functionally manipulated like built-in objects
2.Overriding method of object to string function
repr(obj) function override method:
def __repr__(self):
return 'string'
str(obj) function override method:
def __str__(self):
return 'string'
For example see:
mynumber.py
student.py
str(obj) Function call method description:
1. call first obj.__str__() method value.
2. if obj.__str__()method does not exist,then tune
use obj.__repr__() method value
3. if it doesn't exist anymore obj.__repr__()method.then call object
Category__repr__method value.
1. Built-in function rewrite
Built-in function override method name Function name __abs__(self) abs(obj) function __len__(self) len(obj) function __reversed__(self) reversed(obj) __round__(self) round(obj) For example see: len_overwrite.py
2. Value conversion function rewrite
Numeric conversion function rewrite method name Function name __complex__(self) complex(obj) __int__(self) int(obj) __float__(self) float(obj) __bool__(self) bool(obj) For example see: mynumber2.py
3. Boolean test function bool(obj) function rewrite
boolean test function bool(obj) function rewrite
effect:
used for bool(obj) function value:
used for if in the truth expression of the statement
used for while in the truth expression of the statement
illustrate:
1. Priority call obj.__bool__() method to get value
2. when not there obj.__bool__() method,use
obj.__len__() boolean value to determine whether the return value is zero
3. when not there__len__() method,return directly True
For example see:
bool.py
8. Object property management functions
Object property management functions
getattr(obj, name[, default]) get from an object
properties of objects; getattr(x, 'y') Equivalent to x.y;
when the attribute does not exist,if given default parameter,then return
back default,if not given default produces a
indivual AttributeError mistake
hasattr(obj, name) with the given name return object obj Yes
has this property,This approach can avoid
getattr(obj, name)throws an error when
setattr(obj, name, value) to the object obj named
name property set the corresponding value value,
set(x, 'y', v) Equivalent to x.y = v
delattr(obj, name) delete object obj middle name Attributes,
delattr(x, 'y') Equivalent to del x.y
9. Iterators (Advanced)
1.iterator(advanced)
what is an iterator
may pass next(it) The object that the function takes is the iterator
iterator protocol:
The iterator protocol means that objects can use next function get next
item data,Trigger one when there is no next item of data StopIteration
Exception to terminate iteration convention
Implementation method of iterator protocol:
__next__(self) method to implement the iterator protocol
2.what is an iterable object:
means usable iter(obj) The function returns an iterator object(example)
The inner part of the iterable object needs to be defined __iter__(self) method to return
iterator object(example)
For example see:
mylist_iterable.py
practise:
1. Changes to previous student information management procedures
Request to transfer student's grades,Name, age attributes are encapsulated, do not allow
remove Student Function and method access and modification outside the class
2. Implement a system built-in range class with the same function:
class MyRange:
def __init__(self, ....):
...
def __iter__(self):
...
Implement the following functions:
L = list(MyRange(5))
print(L) # [0, 1, 2, 3, 4]
print(sum(MyRange(1, 101))) # 5050
L2 = [x**2 for x in MyRange(1, 10, 3)]
print(L2) # [1, 16, 49]
for x in MyRange(10, 0, -3):
print(x) # 10, 7, 4, 1
day19 review
issubclass(cls, class or tuple)
package
__ Start with private properties and private methods to implement
polymorphism
dynamic and static
inherit,package,polymorphism
multiple inheritance
A subclass inherits from two or more parent classes
__mro__ Method Resolution Order
super(B, b).xxxx()
function rewrite
Enable custom classes to operate using built-in functions
repr __repr__
str __str__
len
abs
round
reversed
int
float
complex
bool
Four attribute-related functions
setattr(obj, name, value)
hasattr(obj, name)
getattr(obj, name [,default])
delattr(obj, name)
iterator
__next__(self) method
Implement the iterator protocol
iterable object
__iter__(self) method
return iterator
Day20 Notes
2.10 Exceptions
1. Exception
abnormal
Exception-Related Statements Review:
try-except
try-finally
raise
assert
2.with statement
3. Environment Manager
environment manager class has __enter__ and __exit__A class with instance methods is called environment manager __enter__will enter with is called when the statement,and return by as variable managed objects __exit__will be leaving with is called when the statement,and can use parameters to Judgment is leaving with Whether an exception occurred during the statement,and make corresponding deal with For example see: with2.py
4. Operator overloading
operator overloading
What is operator overloading
Let the custom class generate the object(example)able to use operations
character to operate
effect:
Let instances of custom classes use operators like built-in objects
Make the program concise and easy to read
Assign operators to new rules for custom objects
1. Arithmetic operator overloading
Arithmetic operator overloading
method name Operator and Expression Description
__add__(self, rhs) self + rhs addition
__sub__(self, rhs) self - rhs subtraction
__mul__(self, rhs) self * rhs multiplication
__truediv__(self, rhs) self / rhs division
__floordiv__(self, rhs) self // rhs floor removal
__mod__(self, rhs) self % rhs Surplus
__pow__(self, rhs) self ** rhs exponentiation
rhs (right hands side) right hand side
For example see:
mynumber1.py
illustrate:
The methods and parameters of operator overloading already have fixed meanings,not recommend
change the original meaning
practise:
Implements the addition of two custom lists
class MyList:
def __init__(self, iterable=()):
...
.....
L1 = MyList(range(1, 4))
L2 = MyList([4, 5, 6])
L3 = L1 + L2
print(L3) # MyList([1, 2, 3, 4, 5, 6])
L4 = L2 + L1
print(L4) # MyList([4, 5, 6, 1, 2, 3])
L5 = L1 * 2
print(L5) # MyList([1, 2, 3, 1, 2, 3])
# think:
L6 = 2 * L2 # Can it? Why?
2. Overloading of reverse arithmetic operators
Overloading of reverse arithmetic operators
When the left side of the operator is a built-in type,Arithmetic for custom types on the right
during operation,Will appear TypeError mistake
Operator overloading due to inability to modify code for built-in types,At this time need
Overloading is done using reverse arithmetic operator overloading
method name Operator and Expression Description
__radd__(self, lhs) lhs + self addition
__rsub__(self, lhs) lhs - self subtraction
__rmul__(self, lhs) lhs * self multiplication
__rtruediv__(self, lhs) lhs / self division
__rfloordiv__(self, lhs) lhs // self floor removal
__rmod__(self, lhs) lhs % self Surplus
__rpow__(self, lhs) lhs ** self exponentiation
For example see:
code/mylist.py
3. Compound assignment arithmetic operator overloading
Compound assignment arithmetic operator overloading with compound assignment arithmetic operators x += y For example,this operator takes precedence transfer x.__iadd__(y) method.if there is not__iadd__method When the conjunctive assignment operator is disassembled into x = x + y and then call x = x.__add__(y) method,if it doesn't exist anymore__add__method will trigger TypeError abnormal The same rules apply to other compound assignment arithmetic operators method name Operator and Expression Description __iadd__(self, rhs) self += rhs addition __isub__(self, rhs) self -= rhs subtraction __imul__(self, rhs) self *= rhs multiplication __itruediv__(self, rhs) self /= rhs division __ifloordiv__(self, rhs) self //= rhs floor division __imod__(self, rhs) self %= rhs Surplus __ipow__(self, rhs) self **= rhs exponentiation For example see: mylist2.py
question:
# ---- Program 1 is implemented as a list -------
L = [1, 2, 3]
def f1(lst):
lst += [4, 5, 6]
f1(L)
print(L) # [1, 2, 3, 4, 5, 6]
# -----The program is implemented with tuples --------
L = (1, 2, 3)
def f1(lst):
lst += (4, 5, 6)
f1(L)
print(L) # (1, 2, 3)
4. Overloading of comparison operators
Overloading of comparison operators: method name Operator and Expression Description __lt__(self, rhs) self < rhs less than __le__(self, rhs) self <= rhs less than or equal to __gt__(self, rhs) self > rhs more than the __ge__(self, rhs) self >= rhs greater or equal to __eq__(self, rhs) self == rhs equal __ne__(self, rhs) self != rhs not equal to
5. Bitwise operator overloading
Bitwise operator overloading: method name Operator and Expression Description __and__(self, rhs) self & rhs bit and __or__(self, rhs) self | rhs bit or __xor__(self, rhs) self ^ rhs bit XOR __lshift(self, rhs) self << rhs shift left __rshift(self, rhs) self >> rhs move right
6. Reverse bitwise operator overloading
Reverse bitwise operator overloading: method name Operator and Expression Description __rand__(self, lhs) lhs & self bit and __ror__(self, lhs) lhs | self bit or __rxor__(self, lhs) lhs ^ self bit XOR __rlshift(self, lhs) lhs << self shift left __rrshift(self, lhs) lhs >> self move right
7. Compound assignment bitwise operator overloading
Compound assignment bitwise operator overloading: method name Operator and Expression Description __iand__(self, rhs) self &= rhs bit and __ior__(self, rhs) self |= rhs bit or __ixor__(self, rhs) self ^= rhs bit XOR __ilshift(self, rhs) self <<= rhs shift left __irshift(self, rhs) self >>= rhs move right
8. Unary operator overloading
Unary operator overloading:
method name Operator and Expression Description
__neg__(self) - self negative
__pos__(self) + self Positive sign
__insert__(self) ~ self Negate
grammar:
class class name:
def __xxx__(self):
....
For example see:
mylist4.py
9.in / not in operator overloading
in / not in operator overloading:
method name Operators and Expressions
__contains__(self, e) e in self
For example see:
mylist5.py
10. Overloading of indexing and slicing operators
Overloading of indexing and slicing operators: L[0] L[::2] method name Operator and Expression Description __getitem__(self, i) x = self[i] value __setitem__(self, i, v) self[i] = v assign __delitem__(self, i) del self[i] drop index For example see: mylist6.py
5.slice constructor
slice Constructor
effect:
for creating a slice slice object,This object stores a slice
starting value of,end value and step size information,Default is None
Format:
slice(start=None, stop=None, step=None)
slice object properties
s.start The starting value of the slice defaults to None
s.stop the end value of the slice,The default is None
s.step step size of slice,The default is None
For example see:
mylist7.py
6. Feature property @property
characteristic attribute @property
Implement what other languages have getter and setter Function
effect:
used to simulate a property
pass@property Decorators can assign and get values to mocked properties
to control
For example see:
property.py
7.PEP8 encoding specification
PEP8 Coding Standards
Documentation see:
python_base_docs_html/PEP8 Coding Standards.html
return
return default, if default is not given, a
AttributeError errors
hasattr(obj, name) returns the object obj with the given name is
Whether there is this property, this approach can avoid
throws error when getattr(obj, name)
setattr(obj, name, value) gives the name of the object obj
The attribute of name sets the corresponding value value,
set(x, 'y', v) is equivalent to x.y = v
delattr(obj, name) delete the name attribute in the object obj,
delattr(x, 'y') is equivalent to del x.y
#### 9. Iterators (Advanced)
```python
1.iterator(advanced)
what is an iterator
may pass next(it) The object that the function takes is the iterator
iterator protocol:
The iterator protocol means that objects can use next function get next
item data,Trigger one when there is no next item of data StopIteration
Exception to terminate iteration convention
Implementation method of iterator protocol:
__next__(self) method to implement the iterator protocol
2.what is an iterable object:
means usable iter(obj) The function returns an iterator object(example)
The inner part of the iterable object needs to be defined __iter__(self) method to return
iterator object(example)
For example see:
mylist_iterable.py
practise:
1. Changes to previous student information management procedures
Request to transfer student's grades,Name, age attributes are encapsulated, do not allow
remove Student Function and method access and modification outside the class
2. Implement a system built-in range class with the same function:
class MyRange:
def __init__(self, ....):
...
def __iter__(self):
...
Implement the following functions:
L = list(MyRange(5))
print(L) # [0, 1, 2, 3, 4]
print(sum(MyRange(1, 101))) # 5050
L2 = [x**2 for x in MyRange(1, 10, 3)]
print(L2) # [1, 16, 49]
for x in MyRange(10, 0, -3):
print(x) # 10, 7, 4, 1
day19 review
issubclass(cls, class or tuple)
package
__ Start with private properties and private methods to implement
polymorphism
dynamic and static
inherit,package,polymorphism
multiple inheritance
A subclass inherits from two or more parent classes
__mro__ Method Resolution Order
super(B, b).xxxx()
function rewrite
Enable custom classes to operate using built-in functions
repr __repr__
str __str__
len
abs
round
reversed
int
float
complex
bool
Four attribute-related functions
setattr(obj, name, value)
hasattr(obj, name)
getattr(obj, name [,default])
delattr(obj, name)
iterator
__next__(self) method
Implement the iterator protocol
iterable object
__iter__(self) method
return iterator
Day20 Notes
2.10 Exceptions
1. Exception
abnormal
Exception-Related Statements Review:
try-except
try-finally
raise
assert
2.with statement
3. Environment Manager
environment manager class has __enter__ and __exit__A class with instance methods is called environment manager __enter__will enter with is called when the statement,and return by as variable managed objects __exit__will be leaving with is called when the statement,and can use parameters to Judgment is leaving with Whether an exception occurred during the statement,and make corresponding deal with For example see: with2.py
4. Operator overloading
operator overloading
What is operator overloading
Let the custom class generate the object(example)able to use operations
character to operate
effect:
Let instances of custom classes use operators like built-in objects
Make the program concise and easy to read
Assign operators to new rules for custom objects
1. Arithmetic operator overloading
Arithmetic operator overloading
method name Operator and Expression Description
__add__(self, rhs) self + rhs addition
__sub__(self, rhs) self - rhs subtraction
__mul__(self, rhs) self * rhs multiplication
__truediv__(self, rhs) self / rhs division
__floordiv__(self, rhs) self // rhs floor removal
__mod__(self, rhs) self % rhs Surplus
__pow__(self, rhs) self ** rhs exponentiation
rhs (right hands side) right hand side
For example see:
mynumber1.py
illustrate:
The methods and parameters of operator overloading already have fixed meanings,not recommend
change the original meaning
practise:
Implements the addition of two custom lists
class MyList:
def __init__(self, iterable=()):
...
.....
L1 = MyList(range(1, 4))
L2 = MyList([4, 5, 6])
L3 = L1 + L2
print(L3) # MyList([1, 2, 3, 4, 5, 6])
L4 = L2 + L1
print(L4) # MyList([4, 5, 6, 1, 2, 3])
L5 = L1 * 2
print(L5) # MyList([1, 2, 3, 1, 2, 3])
# think:
L6 = 2 * L2 # Can it? Why?
2. Overloading of reverse arithmetic operators
Overloading of reverse arithmetic operators
When the left side of the operator is a built-in type,Arithmetic for custom types on the right
during operation,Will appear TypeError mistake
Operator overloading due to inability to modify code for built-in types,At this time need
Overloading is done using reverse arithmetic operator overloading
method name Operator and Expression Description
__radd__(self, lhs) lhs + self addition
__rsub__(self, lhs) lhs - self subtraction
__rmul__(self, lhs) lhs * self multiplication
__rtruediv__(self, lhs) lhs / self division
__rfloordiv__(self, lhs) lhs // self floor removal
__rmod__(self, lhs) lhs % self Surplus
__rpow__(self, lhs) lhs ** self exponentiation
For example see:
code/mylist.py
3. Compound assignment arithmetic operator overloading
Compound assignment arithmetic operator overloading with compound assignment arithmetic operators x += y For example,this operator takes precedence transfer x.__iadd__(y) method.if there is not__iadd__method When the conjunctive assignment operator is disassembled into x = x + y and then call x = x.__add__(y) method,if it doesn't exist anymore__add__method will trigger TypeError abnormal The same rules apply to other compound assignment arithmetic operators method name Operator and Expression Description __iadd__(self, rhs) self += rhs addition __isub__(self, rhs) self -= rhs subtraction __imul__(self, rhs) self *= rhs multiplication __itruediv__(self, rhs) self /= rhs division __ifloordiv__(self, rhs) self //= rhs floor division __imod__(self, rhs) self %= rhs Surplus __ipow__(self, rhs) self **= rhs exponentiation For example see: mylist2.py
question:
# ---- Program 1 is implemented as a list -------
L = [1, 2, 3]
def f1(lst):
lst += [4, 5, 6]
f1(L)
print(L) # [1, 2, 3, 4, 5, 6]
# -----The program is implemented with tuples --------
L = (1, 2, 3)
def f1(lst):
lst += (4, 5, 6)
f1(L)
print(L) # (1, 2, 3)
4. Overloading of comparison operators
Overloading of comparison operators: method name Operator and Expression Description __lt__(self, rhs) self < rhs less than __le__(self, rhs) self <= rhs less than or equal to __gt__(self, rhs) self > rhs more than the __ge__(self, rhs) self >= rhs greater or equal to __eq__(self, rhs) self == rhs equal __ne__(self, rhs) self != rhs not equal to
5. Bitwise operator overloading
Bitwise operator overloading: method name Operator and Expression Description __and__(self, rhs) self & rhs bit and __or__(self, rhs) self | rhs bit or __xor__(self, rhs) self ^ rhs bit XOR __lshift(self, rhs) self << rhs shift left __rshift(self, rhs) self >> rhs move right
6. Reverse bitwise operator overloading
Reverse bitwise operator overloading: method name Operator and Expression Description __rand__(self, lhs) lhs & self bit and __ror__(self, lhs) lhs | self bit or __rxor__(self, lhs) lhs ^ self bit XOR __rlshift(self, lhs) lhs << self shift left __rrshift(self, lhs) lhs >> self move right
7. Compound assignment bitwise operator overloading
Compound assignment bitwise operator overloading: method name Operator and Expression Description __iand__(self, rhs) self &= rhs bit and __ior__(self, rhs) self |= rhs bit or __ixor__(self, rhs) self ^= rhs bit XOR __ilshift(self, rhs) self <<= rhs shift left __irshift(self, rhs) self >>= rhs move right
8. Unary operator overloading
Unary operator overloading:
method name Operator and Expression Description
__neg__(self) - self negative
__pos__(self) + self Positive sign
__insert__(self) ~ self Negate
grammar:
class class name:
def __xxx__(self):
....
For example see:
mylist4.py
9.in / not in operator overloading
in / not in operator overloading:
method name Operators and Expressions
__contains__(self, e) e in self
For example see:
mylist5.py
10. Overloading of indexing and slicing operators
Overloading of indexing and slicing operators: L[0] L[::2] method name Operator and Expression Description __getitem__(self, i) x = self[i] value __setitem__(self, i, v) self[i] = v assign __delitem__(self, i) del self[i] drop index For example see: mylist6.py
5.slice constructor
slice Constructor
effect:
for creating a slice slice object,This object stores a slice
starting value of,end value and step size information,Default is None
Format:
slice(start=None, stop=None, step=None)
slice object properties
s.start The starting value of the slice defaults to None
s.stop the end value of the slice,The default is None
s.step step size of slice,The default is None
For example see:
mylist7.py
6. Feature property @property
characteristic attribute @property
Implement what other languages have getter and setter Function
effect:
used to simulate a property
pass@property Decorators can assign and get values to mocked properties
to control
For example see:
property.py
7.PEP8 encoding specification
PEP8 Coding Standards
Documentation see:
python_base_docs_html/PEP8 Coding Standards.html