author：Once Day date:2022 year 2 month 16 Japan
The purpose of this document is to summarize the relevant contents , Scattered knowledge is difficult to remember and learn .
This document is based on windows platform .
View a full range of documents ：python Basics _CSDN Blog .
The list is Python One of the most basic and commonly used data structures in . Each element in the list is assigned a number as an index , Used to indicate the position of the element in the list . The index of the first element is 0, The second index is 1, And so on .
Python The list is an ordered and repeatable collection of elements , Can be nested 、 iteration 、 modify 、 Fragmentation 、 Additional 、 Delete , Member judgment .
From a data structure point of view ,Python The list of is a generalized table , And each location holds a pointer to the object .
Python It also supports negative index values , This kind of index counts right to left , let me put it another way , Count from the last element , From index value -1 Start .
nonelist=[] # An empty list
numbers=[1,2,3,4,5,6] # list
mylist=[1,'b',[1,5],'ssdd'] # The list can be inlaid , And other data objects .
The elements in the list , It can be any other type of data , Multi level nested list , The number of elements is unlimited .
The list can be modified , But tuples and strings cannot be modified .
>>> s=['h','e','l','l','o',',','w','o','r','l','d','!']
>>> s[1]
'e' # The first element is the index value 0
>>> s[-1]
'!' # Minus sign from right to left .
>>> s[12]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: list index out of range # Accessing beyond the index value will throw an exception
Accessing elements in a specific scope , Slicing does not modify the original list , You can save the result to a new variable , Therefore, slicing is also a safe operation , It is often used to copy a list .
>>> n=[1,2,3,4,5,6,7,8,9]
>>> n[2:4]
[3,4] # The first index specifies the start （ Be included in ）, The second index specifies the end , Not to be included .
>>> n[7:9]
[8,9] # Include the last element with the imaginary tenth element .
>>> n[-3:-1]
[7,8] # You can use plural indexes .
>>> n[-3:0]
[] # Empty sequence , The second index should follow the first index .
>>> n[-3:]
[7,8,9] # Omit the second sequence , All the following elements are included by default
>>> n[:2]
[1,2] # Omit the first index , All the previous elements are included by default , Note that the last index is not included
>>> n[:]
[1,2,3,4,5,6,7,8,9] # Contains all elements
# Change the step size , The default is 1.
>>> n[0:9:2]
[1,3,5,7,9] # In steps of 2, Take one from every other number .
>>> n[9:0:-2]
[8,6,4,2] # Extract elements from right to left , The first index is larger than the second index , But the step size is negative , So it can run
>>> n[::-2]
[8,6,4,2] # It can also be successful ！！！
use + Connect Same type Sequence ！
>>> [1,2,3]+[4,5,6]
[1,2,3,4,5,6]
Repetitive sequence N Time
>>> [12]*5
[12,12,12,12,12]
>>> [None]*3
[None,None,None] # Nothing there? -None
in Operator , Boolean operator , return True or False
>>> s=['h','e','l','l','o',',','w','o','r','l','d','!']
>>> 'h' in s
True
>>> for x in [1, 2, 3]: print(x)
1
2
3
Index assignment
>>> nums=[1,2,3,4,5]
>>> nums[2]=8 # You can't assign a value to an element that doesn't exist （ Otherwise, the report will be wrong ）
>>> nums
[1,2,8,4,5]
Slice assignment
The step size is not 1 The number of elements should be considered to match
>>> name=list("onceday")
['o','n','c','e','d','a','y'] # May by list Function directly creates
>>> name[4:]=list('DAY')
['o','n','c','e','D','A','Y'] # On the index 5 To the end of the value assignment
# You can change the length of the list
>>> name[4:]=list('d')
['o','n','c','e','d']
# You can insert elements
>>> name[1:1]=list("eeee")
['o','e','e','e','e','n','c','e','d']
# You can also clear elements
>>> name[1:5]=[]
name=['o','n','c','e','d']
The step size is not 1 The slice assignment of can also be performed , Including negative numbers
Use del sentence
>>> names=['asd','zxc','qwe']
>>> del names[1]
['asd','qwe']
None of these operations will modify the list itself , It belongs to safe operation .max、min stay Python3 in , You can't compare the sizes of different types of objects .
Lists can nest lists , Form a multidimensional list , Shaped like a matrix . The reference method of its element is list[i][j][k]…. Of course , You can also nest other data types .
>>> a = [[1,2,3],[4,5,6],[7,8,9]]
>>> a[0][1]
2
>>> a = [[1,2,3],[4,5,6],[7,8,9],{
"k1":"v1"}]
>>> a[3]["k1"]
'v1'
nums=[1,2,3,4,5,6]
nums.append(4) # hold 4 Add to the end of the list
#nums=[1,2,3,4,5,6,4]
nums.clear() # clear list
#nums=[]
a=[1,2,3,4]
b=a # Regular replication simply b Associated to the same storage space
b[1]=4
#a=[1,4,3,4] a The value in has also changed
c=[1,2,3]
d=c.copy() # A copy will be created
d[1]=4
#c=[1,2,3] # here c The value in has not changed
#d=[1,4,3]
['aa','ss','dd','cc','aa'].count('aa') # Calculates how many times the specified element appears .
#2 Time
e=[1,2,3]
f=[4,5,6]
e.extend(f) # Append multiple values to the end of the list
#e=[1,2,3,4,5,6]
e=e+f # Splicing , A new copy will be created , Low efficiency .
a[len(a):]=b # Slice assignment , Effect and extend identical .
string=['aa','dd','ff','ss','aa']
string.index('aa') # Find the index of the first occurrence of the specified value in the list
#0, If there is no element to search , May be an error .
numbers[1,2,3,4,5,6]
numbers.insert(2,'right') # Insert an object into the list
#numbers=[1,2,'right',3,4,5,6]
numbers[2:2]=['right'] # Effect and insert identical
x=[1,2,3]
x.pop() # Delete the last element , And return this element
x.pop(0) # Delete the first 1 Elements , And return this value .
#pop and append Stack can be built , Last in, first out （LIFO）, fifo （FIFO）
x=['a','s','d','a']
x.remove('a') # Delete the first element with the specified value , No return value
# x=['s','d','a']
# Delete unknown element （ Not in the list ） Will be an error .
x=[1,2,3,4]
x.reverse() # Arrange the elements in the list in reverse order
#x=[4,3,2,1]
x=[2,1,5,3,4]
x.sort() # Sort the list in place , No return value
#x=[1,2,3,4,5]
# Keep the original list , And save the sorted list to a new list
x=[2,1,3]
y=x.copy()
y.sort()
#x=[2,1,3]
#y=[1,2,3]
x=[3,2,1,4,5]
y=sorted(x) # Return a sequence
#x=[3,2,1,4,5]
#y=[1,2,3,4,5]
#sort and sorted Acceptable parameters key and reverse, Not for the time being
