Python common operations and Derivations
1, Public operation
-
operator
-
Public method
-
Container type conversion
1, Operator
operator | describe | Supported container types |
---|---|---|
+ | merge | String, list, tuple |
* | copy | String, list, tuple |
in | Does the element exist | String, list, tuple, dictionary |
not in | Does the element not exist | String, list, tuple, dictionary |
1.1 +
#1. String str1='aa' str2='bb' str3=str1+str2 print(str3) #aabb # 2. List list1=[1,2] list2=[10,20] list3=list1+list2 print(list3) #[1, 2, 10, 20] # 3. Tuple t1=(1,2) t2=(10,20) t3=t1+t2 print(t3) #(1, 2, 10, 20)
1.2 *
#1. String print('-'*10) # 2. List list1=['hello'] print(list1*4) # 3. Tuple t1=('world',) print(t1*4)
1.3 in or not in
#1. String print('a' in 'abcd') print('a' not in 'abcd') # 2. List list1=['a','b','c''d'] print('a' in list1) print('a' not in list1) # 3. Tuple t1=('a','b','c','d') print('aa' in t1) print('aa' not in t1)
2, Public method
function | describe |
---|---|
len() | Calculate the number of elements in the container |
Del or del() | delete |
max() | Returns the maximum value of the element in the container |
min() | However, the minimum value of the element in the container will be |
range(start,end,step) | Generate the number from star to end in step for the for loop |
enumerate() | The function is used to combine a traversable data object (such as list, tuple or string) into an index sequence, and list data and data subscripts at the same time. It is generally used in the for loop |
2.1 len()
#1. String str1='abcdefg' print(len(str1)) # 2. List list1=[10,20,30,40] print(len(list1)) # 3. Tuple t1=(10,20,30,40) print(len(t1)) # 4. Assemble s1={10,20,30} print(len(s1)) # 5. Dictionary dict={'name':'Rose','age':18} print(len(dict))
2.2 del()
#1. String str1='abcdefg' del str1 print(str1) # 2. List list1=[10,20,30,40] del(list1[0]) print(list1) #[20, 30, 40]
2.3 max()
#1. String str1='abcdefg' print(max(str1))#g # 2. List list1=[10,20,30,40] print(max(list1))#40
2.4 min()
#1. String str1='abcdefg' print(min(str1))#a # 2. List list1=[10,20,30,40] print(min(list1))#10
2.5 range()
for i in range(1,10,1): print(i) #1 2 3 4 5 6 7 8 9 for i in range(1,10,2): print(i) # 1 3 5 7 9 for i in range(10): print(i) #0 1 2 3 4 5 6 7 8 9
2.6 enumerate()
- grammar
enumerate(Traversable objects, start=0)
Note: the start parameter with is used to set the starting value of the subscript of traversal data, which is 0 by default.
- experience
list1=['a','b','c','d','e'] for i in enumerate(list1): print(i) for index,char in enumerate(list1,start=1): print(f'The subscript is{index},The corresponding character is{char}')
3, Container type conversion
3.1 tuple()
Function: convert a sequence into tuples
list1=[10,20,30,40,50,20] s1={100,200,300,400,500,} print(tuple(list1)) print(tuple(s1))
3.2 list()
Function: convert a sequence into a list
t1=('a','b','c','d','e') s1={100,200,300,400,500} print(list(t1)) print(list(s1))
3.3 set()
Function: convert a sequence into a set
list1 = [10, 20, 30, 40, 50, 20] t1 = ('a', 'b', 'c', 'd', 'e') print(set(list1)) print(set(t1))
5, Derivation
1, List derivation
As: Use an expression to create a regular list or controls a regular list.
The following table derivation formula is called list formation formula
1.1 experience
Create a requirement list of 0-10
- while loop implementation
#1. Prepare an empty list list1 = [] # 2. Write cycle, and add numbers to the empty list list1 in turn i = 0 while i < 10: list1.append(i) i += 1 print(list1)
- for loop implementation
list1 = [] for i in range(10): list1.append(i) print(list1)
- List derivation implementation
list1 = [i for i in range(10)] print(list1)
1.2 list derivation with if
Requirement: create an even list of 0-10
- Method 1: range() step implementation
list1 = [i for i in range(0, 10, 2)] print(list1)
- Method 2: if implementation
list1 = [i for i in range(10) if i % 2 == 0] print(list1)
1.3 list derivation of multiple for loops
Requirement creation list is as follows:
[(1, 0), (1, 1), (1, 2), (2, 0), (2, 1), (2, 2)]
- The code is as follows:
list1 = [(i, j) for i in range(1, 3) for j in range(3)] print(list1)
2, Dictionary derivation
Think: if there are two lists
list1 = ['name', 'age', 'gender'] list2 = ['Tom', 20, 'man']
How to quickly merge into one dictionary?
Answer: Dictionary derivation
Dictionary derivation function: quickly merge the list or extract the target data in the dictionary
2.1 experience
1. Create a dictionary: the dictionary key is a 1-5 number, and the value is the power of the number
dict1 = {i: i**2 for i in range(1, 5)} print(dict1) # {1: 1, 2: 4, 3: 9, 4: 16}
2. Merge the two lists into one dictionary
list1 = ['name', 'age', 'gender'] list2 = ['Tom', 20, 'man'] dict1 = {list1[i]: list2[i] for i in range(len(list1))} print(dict1)
3. Extract target data from dictionary
counts = {'MBP': 268, 'HP': 125, 'DELL': 201, 'Lenovo': 199, 'acer': 99} # Demand: extract dictionary data with the number of computers above 200 or more count1 = {key: value for key, value in counts.items() if value >= 200} print(count1) # {'MBP': 268, 'DELL': 201}
III Set derivation
Requirement: create a set with data to the power of 2 in the list below
list1 = [1, 1, 2]
The code is as follows:
list1 = [1, 1, 2] set1 = {i ** 2 for i in list1} print(set1) # {1, 4}
Note: the collection has the function of data De duplication
4, Summary
- Function of derivation: simplify code
- Writing method of derivation
# Derivation of column table [xx for xx in range()] # Dictionary derivation {xx1: xx2 for ... in ...} # Set derivation {xx for xx in ...}