b station Dane python class study notes

P50 Python Basics-5.1 Course Content Review

1. Review day04

"""
    day04 review
    sentence
        loop statement
            for　+ range(): fixed number of cycles
            while:loop with conditional execution　

            range(start,Finish,step size)
                range(2,6,2)->2 4
                range(2)->0 1
                range(2,2)->

    container
        string str:Immutable　　encoded value　utf－８　　
            literal value
                apostrophe　Double quotes　triple quotes (what you see is what you get)
                Escapes \character
                string formatting
                "..."+variable 1+".."+Variable 2+".."
                "...%s..%f.."%(variable 1,Variable 2)

        common operation
            mathematical operator +   *
            member operator element in container
            index:Locating a single element
            Slicing: positioning multiple elements
            function:len(container) length
"""
name = 'Daqiang'
name = "cockroach"
print(name)#cockroach

P51 Python Basics-5.2 Homework Analysis

1. Exercise 1: Formatting and printing

"""
3.  According to the following format, output variables name = "goku",age = 800,score = 99.5
     My name is xx,age is xx,result is xx. 
"""

name = "goku"
age = 800
score = 99.5
message = "My name is%s,age is%d,result is%.1f. " % (name, age, score)
print(message)

2. Exercise 2: for loop

"""
4.　Get an integer as the side length in the console．
　　Print a rectangle according to its side length．
   Example: 4
       ****
       *  *
       *  *
       ****

       6
       ******
       *    *
       *    *
       *    *
       *    *
       ******
"""

number = int(input("Please enter an integer:"))  # 4

print("*" * number)

for item in range(number - 2):  #
    print("*" + " " * (number - 2) + "*")

print("*" * number)

3. Exercise 3: String Slicing

"""
5.Enter a string in the console to determine whether it is a palindrome．
  judgment rule:Forward and reverse are the same．
  　　　Shanghai tap water comes from the sea
"""

message = "Shanghai tap water comes from the sea"
if message == message[::-1]:
    print("is a palindrome")
else:
    print("not a palindrome")

4. Exercise 4: while loop

"""
6. (expand)A small ball from 100ｍdrop from height
    　　Each bounce back to half the original height．
    　　Calculation: how many times it bounces up in total (minimum bounce height 0.01ｍ)．
            how many meters in total
"""

height = 100
count = 0
# Passed distance
distance = height
# The height before the bounce is greater than the minimum bounce height
# while height > 0.01:
# The bounce height is greater than the minimum bounce height
while height / 2 > 0.01:
    count += 1
    # pop up
    height /= 2
    print("No.%d The height of the second bounce is%f." % (count, height))
    # Cumulative take-off/fall height
    distance += height * 2

print("total bounce%d Second-rate" % count)
print("The total distance traveled is%.2f" % distance)

P52~53 Python Basics-5.3&5.4 List Introduction 01&02

1. Definition

A mutable sequence container consisting of a sequence of variables.

2. Basic operation

Create list:

ListName = []
listName = list( iterable object)

Add element:

listname.append( element)
list.insert( index, element)

Positioning elements:

index, slice

Iterate over the list:

Forward:
for variable name in list name:
	The variable name is the element
	Reverse:
for index name in range(len(list name)-1,-1,-1):
	list name[index name]is the element

Remove element:

listname.remove( element)
del listName [index or slice]

3. Example code

# 1. Create a list
# null
list01 = []
list01 = list()

# Defaults
list02 = ["Goku", 100, True]
list02 = list("I'm Monkey King")

# 2. Get the element
# index
print(list02[2])  # together
# slice
print(list02[-4:])  # ['Qi', 'Heaven', 'Big', 'Holy']

# 3. Add elements
# Append (add at the end)
list02.append("Bajie")
# Insert (add at specified position)
list02.insert(1, True)  # Add True at index 1 (second)

# 4. Delete elements
# delete by element
list02.remove("yes")
# delete by location

del list02[0]
print(list02)

# 5. Define elements, purpose: to add, delete, modify and check elements.
# slice
del list02[1:3]
print(list02)
# [True, 'Big', 'Holy', 'Bajie']
# [True, 'a', 'b', 'Bajie']
list02[1:3] = ["a", "b"]
# [True, 'Bajie']
# list02[1:3] = []
print(list02)

# traverse the list
# Get all elements in the list
for item in list02:
    print(item)

# Get all elements in reverse order
# Not recommended
# list02[::-1] takes elements by slicing and will recreate a new list.
# for item in list02[::-1]:
#     print(item)

# 3  2  1  0
for i in range(len(list02) - 1, -1, -1):
    print(list02[i])

# -1  -2  -3  -4
for i in range(-1, -len(list02) - 1, -1):
    print(list02[i])

P54 Python Basics-5.5 List Exercises

1. Exercise 1

"""
    Exercise 1:
    Enter in the console, your favorite characters in Journey to the West.
    Enter an empty string, print(A row)all characters.
"""

list_person = []
# entry process
while True:
    str_input = input("Enter your favorite characters in Journey to the West:")
    if str_input == "":
        break
    list_person.append(str_input)

# output process
for item in list_person:
    print(item)

2. Exercise 2

'''
# Exercise: Enter in the console, all student grades.
# Enter an empty string to print (one per line) all grades.
# Print the highest score, print the lowest score, and print the average score.
'''

list_score = []
# entry process
while True:
    str_score = input("Please enter grades:")
    if str_score == "":
        break
list_score.append(int(str_score))  # output process
for item in list_score:
    print(item)

print("Highest score:" + str(max(list_score)))
print("Lowest score:" + str(min(list_score)))
print("The average score:" + str(sum(list_score) / len(list_score)))

P55 Python basics-5.6 practice of entering student names (debugging code)

1. Practice (debugging code)

"""
# Exercise 3:
# Enter in the console, the names of all students.
# If the name is repeated, it will prompt "the name already exists" and will not be added to the list.
# If an empty string is entered, all students are printed in reverse.
"""

list_name = []
while True:
    name = input("Please type in your name:")
    if name == "":
        break
    # Check if variable exists in list
    if name not in list_name:
        list_name.append(name)
    else:
        print("name already exists")

# -1  -2  -3
# 2  1   0
for item in range(-1, -len(list_name) - 1, -1):
    print(list_name[item])

P56 Python Basics-5.7 List Memory Map

memory map 1

list01 = ["Zhang Wuji","Zhao Min"]
list02 = list01
# Modifies the first element of the list
list01[0] = "Mowgli"
print(list02[0])

memory map 2

list01 = ["Zhang Wuji","Zhao Min"]
list02 = list01
# The modified list01 variable
list01 = ["Mowgli"]
print(list02[0])#Zhang Wuji

Memory Figure 3

list01 = [800,1000]
# Getting elements by slice creates a new list.
list02 = list01[:]
list01[0] = 900
print(list02[0])#?800
list01 = [500]
print(list02[0])#?800

Memory Figure 4

# list of lists
list01 = [800,[1000,500]]
list02 = list01
list01[1][0] = 900
print(list02[1][0])#?900

Memory Figure 5 (shallow copy case of list)

# list of lists
list01 = [800,[1000,500]]
list02 = list01[:]
list01[1][0] = 900
print(list02[1][0])#?900

P57 Python Basics-5.8 Deep Copy and Shallow Copy

1. Deep copy and shallow copy

Shallow copy: During the copying process, only one layer of variables is copied, and the copying process of objects bound to deep variables will not be copied.
Deep copy: Copy the entire dependent variable.

shallow copy

list01 = [800,[1000,500]]
# shallow copy
# list02 = list01[:]
list02 = list01.copy() #Equivalent to the slice from the previous line
list01[1][0] = 900
print(list02[1][0])#?900

deep copy

import copy

list01 = [800,[1000,500]]
# deep copy
list02 =copy.deepcopy(list01)
list01[1][0] = 900
print(list02[1][0])#?

Deep copy memory map

P58 Python Basics-5.9 List memory graph exercise

1. Exercise 1

"""
    Exercise 1:
        will list[54,25,12,42,35,17]middle,
        Numbers greater than 30 are stored in another list.
        and draw a memory map.
"""
# Exercise 1:
list01 = [54, 25, 12, 42, 35, 17]
list02 = []
for item in list01:
    if item > 30:
        list02.append(item)
print(list02)

memory map

2. Exercise 2

"""
    Exercise 2:
        Enter 5 numbers in the console,
        Print the maximum value (not applicable max).
"""
# Exercise 2:
# assumed maximum
max_value = 0
for item in range(5):
    number = int(input("Please enter the No.%d numbers:" % (item + 1)))
    if max_value < number:
        max_value = number
print(max_value)

P59 Python Basics-5.10 Exercises for calculating the maximum value and deleting elements

1. Calculate the maximum value

Sample code (bubble sort idea)

# Exercise 3:
# In the list [54, 25, 12, 42, 35, 17], pick the largest value (max is not used).
list01 = [54, 25, 12, 42, 100, 17]
# Assuming the first is the largest
max_value = list01[0]
# Compare with the following (starting from the second) element
# 1 2 3 4 5
for i in range(1, len(list01)):
    if max_value < list01[i]:
        # If a larger one is found, replace the assumed one.
        max_value = list01[i]

print(max_value)

2. Delete elements

Exercise 4: In the list [9, 25, 12, 8], delete numbers greater than 10.

Principle of deletion

wrong way to delete

list01 = [9, 25, 12, 8]
for item in list01:
    if item > 10:
        list01.remove(item)
print(list01)
'''
The result is [9, 12, 8]，12 not deleted
 The reason is that when deleting from left to right, the position of the deleted element will be filled by the following element, so that the filled element will not be traversed
 The purpose of doing this for memory is to improve memory utilization, otherwise there will be no shit in the latrine
'''

remove() deletes the principle memory map

The correct way to delete: from right to left (from the end to the beginning)

list01 = [9, 25, 12, 8]
#3 2  1 0
#-1 -2 -3 -4
for i in range(len(list01)-1,-1,-1):
    if list01[i] > 10:
        list01.remove(list01[i])
print(list01)

P60 Python Basics-5.11 List and String Comparison and Homework Assignment

1. List VS String

1. Both lists and strings are sequences, and there is an order relationship between elements.
2. Strings are immutable sequences and lists are mutable sequences.
3. Each element in a string can only store characters, while a list can store any type.
4. Both lists and strings are iterable objects.
5. function:
   Concatenates multiple strings into one.
   result = "connector".join( list)
   Split a string into multiples.
   list = "a-b-c-d".split("separator")

2. String splicing optimization scheme

'''
 Requirements: According toｘｘlogic, splicing a string.
 "0123456789"
'''

'''
Method 1: String addition
 Disadvantage: Each loop forms (+=)a new string object,Replace variable references result. 
'''
result = ""
for item in range(10):
    #""
    #"0"
    #"01"
    #"012"
    result = result + str(item)

'''
Method 2: list, join()
Advantages: Each loop only adds strings to the list, and does not create a list object.
'''
list_temp = []
for item in range(10):
    list_temp.append(str(item))
# join : list --> str
result = " ".join(list_temp)
print(type(result))
print(result)

exercise 1

 practise:Loop through input strings in the console,Stop if the input is empty.
     Finally print everything (spliced ​​string).

list_result = []
while True:
    str_input = input("please enter:")
    if str_input == "":
        break
    list_result.append(str_input)

str_result = "".join(list_result)
print(str_result)

4. String splitting (str–>list)

str01 = "Zhang Wuji-Zhao Min-Zhou Zhiruo"
list_result = str01.split("-")
print(list_result)

exercise 2

practise:english word flip
"How are you" -->"you are How"

str01 = "How are you"
list_temp = str01.split(" ")
str_result = " ".join(list_temp[::-1])
print(str_result)