Python列表(List)（python列表list[0][1]）

列表（Lists）就像用其他语言声明的数组一样。列表不一定总是同质的，这使其成为Python中最强大的工具。单个列表可能包含数据类型，例如整数，字符串以及对象。列表是可变的，因此即使在创建后也可以对其进行更改。

Python中的List是有序的，并且有一个确定的计数。列表中的元素按照一定的顺序进行索引，并且列表的索引是在0为第一个索引的情况下完成的。列表中的每个元素在列表中都有其明确的位置，这允许复制列表中的元素，每个元素都有其独特的位置和可信度。

注意：列表是用于保留数据序列并对其进行进一步迭代的有用工具。

创建列表

Python中的列表可以通过将序列放在方括号[]中来创建。与集合不同，list不需要内置函数来创建list。

注意：与集合不同，列表可能包含可变元素。

# Python program to demonstrate  
# Creation of List  
  
# Creating a List 
List = [] 
print("Intial blank List: ") 
print(List) 
  
# Creating a List with  
# the use of a String 
List = ['GeeksForGeeks'] 
print("\nList with the use of String: ") 
print(List) 
  
# Creating a List with 
# the use of multiple values 
List = ["Geeks", "For", "Geeks"] 
print("\nList containing multiple values: ") 
print(List[0])  
print(List[2]) 
  
# Creating a Multi-Dimensional List 
# (By Nesting a list inside a List) 
List = [['Geeks', 'For'] , ['Geeks']] 
print("\nMulti-Dimensional List: ") 
print(List) 

输出：

Intial blank List: 
[]

List with the use of String: 
['GeeksForGeeks']

List containing multiple values: 
Geeks
Geeks

Multi-Dimensional List: 
[['Geeks', 'For'], ['Geeks']]

创建包含多个不同或重复元素的列表

列表可能包含具有不同位置的重复值，因此，在创建列表时，可以将多个不同或重复的值作为序列传递。

# Creating a List with  
# the use of Numbers 
# (Having duplicate values) 
List = [1, 2, 4, 4, 3, 3, 3, 6, 5] 
print("\nList with the use of Numbers: ") 
print(List) 
  
# Creating a List with  
# mixed type of values 
# (Having numbers and strings) 
List = [1, 2, 'Geeks', 4, 'For', 6, 'Geeks'] 
print("\nList with the use of Mixed Values: ") 
print(List) 

输出：

List with the use of Numbers: 
[1, 2, 4, 4, 3, 3, 3, 6, 5]

List with the use of Mixed Values: 
[1, 2, 'Geeks', 4, 'For', 6, 'Geeks']

向列表中添加元素

使用append()方法

可以使用内置的append()函数将元素添加到列表中。使用append()方法一次只能向列表中添加一个元素，如果使用append()方法添加多个元素，则使用循环。元组也可以使用append方法添加到列表中，因为元组是不可变的。与集合不同，还可以使用append()方法将列表添加到现有列表中。

# Python program to demonstrate  
# Addition of elements in a List 
  
# Creating a List 
List = [] 
print("Initial blank List: ") 
print(List) 
  
# Addition of Elements  
# in the List 
List.append(1) 
List.append(2) 
List.append(4) 
print("\nList after Addition of Three elements: ") 
print(List) 
  
# Adding elements to the List 
# using Iterator 
for i in range(1, 4): 
    List.append(i) 
print("\nList after Addition of elements from 1-3: ") 
print(List) 
  
# Adding Tuples to the List 
List.append((5, 6)) 
print("\nList after Addition of a Tuple: ") 
print(List) 
  
# Addition of List to a List 
List2 = ['For', 'Geeks'] 
List.append(List2) 
print("\nList after Addition of a List: ") 
print(List) 

输出：

Initial blank List: 
[]

List after Addition of Three elements: 
[1, 2, 4]

List after Addition of elements from 1-3: 
[1, 2, 4, 1, 2, 3]

List after Addition of a Tuple: 
[1, 2, 4, 1, 2, 3, (5, 6)]

List after Addition of a List: 
[1, 2, 4, 1, 2, 3, (5, 6), ['For', 'Geeks']]

使用insert()方法

append()方法只适用于在列表末尾添加元素，对于在所需位置添加元素，则使用insert()方法。与只接受一个参数的append()不同，insert()方法需要两个参数（位置、值）。

# Python program to demonstrate  
# Addition of elements in a List 
   
# Creating a List 
List = [1,2,3,4] 
print("Initial List: ") 
print(List) 
  
# Addition of Element at  
# specific Position 
# (using Insert Method) 
List.insert(3, 12) 
List.insert(0, 'Geeks') 
print("\nList after performing Insert Operation: ") 
print(List) 

输出：

Initial List: 
[1, 2, 3, 4]

List after performing Insert Operation: 
['Geeks', 1, 2, 3, 12, 4]

使用extend()方法

除了append()和insert()方法之外，还有一个用于添加元素的方法extend()，该方法用于在列表末尾同时添加多个元素。

注意：append()和extend()方法只能在末尾添加元素。

# Python program to demonstrate  
# Addition of elements in a List 
    
# Creating a List 
List = [1,2,3,4] 
print("Initial List: ") 
print(List) 
  
# Addition of multiple elements 
# to the List at the end 
# (using Extend Method) 
List.extend([8, 'Geeks', 'Always']) 
print("\nList after performing Extend Operation: ") 
print(List) 

输出：

Initial List: 
[1, 2, 3, 4]

List after performing Extend Operation: 
[1, 2, 3, 4, 8, 'Geeks', 'Always']

访问列表中的元素

要访问列表项，请参考索引号。使用索引运算符[]访问列表中的项。索引必须是整数。使用嵌套索引访问嵌套列表。

# Python program to demonstrate  
# accessing of element from list 
  
# Creating a List with 
# the use of multiple values 
List = ["Geeks", "For", "Geeks"] 
  
# accessing a element from the  
# list using index number 
print("Accessing a element from the list") 
print(List[0])  
print(List[2]) 
  
# Creating a Multi-Dimensional List 
# (By Nesting a list inside a List) 
List = [['Geeks', 'For'] , ['Geeks']] 
  
# accessing a element from the  
# Multi-Dimensional List using 
# index number 
print("Acessing a element from a Multi-Dimensional list") 
print(List[0][1]) 
print(List[1][0]) 

输出：

Accessing a element from the list
Geeks
Geeks

Acessing a element from a Multi-Dimensional list
For
Geeks

负索引

在Python中，负序列索引表示数组末尾的位置。不必像List[len（List）-3]那样计算偏移量，只需编写List[-3]就足够了。负索引意味着从结尾开始，-1表示最后一项，-2表示第二个最后项等。

List = [1, 2, 'Geeks', 4, 'For', 6, 'Geeks'] 
  
# accessing a element using 
# negative indexing 
print("Acessing element using negative indexing") 
  
# print the last element of list 
print(List[-1]) 
  
# print the third last element of list  
print(List[-3]) 

输出：

Acessing element using negative indexing
Geeks
For

从列表中删除元素

使用remove()方法

可以使用内置的remove()函数从列表中删除元素，但是如果元素不存在于集合中，则会发生错误。Remove()方法一次只删除一个元素，要删除元素范围，则使用迭代器。remove()方法删除指定的项目。

注意：列表中的Remove方法将只删除搜索到的元素的第一个匹配项。

# Python program to demonstrate  
# Removal of elements in a List 
  
# Creating a List 
List = [1, 2, 3, 4, 5, 6,  
        7, 8, 9, 10, 11, 12] 
print("Intial List: ") 
print(List) 
  
# Removing elements from List 
# using Remove() method 
List.remove(5) 
List.remove(6) 
print("\nList after Removal of two elements: ") 
print(List) 
  
# Removing elements from List 
# using iterator method 
for i in range(1, 5): 
    List.remove(i) 
print("\nList after Removing a range of elements: ") 
print(List) 

输出：

Intial List: 
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

List after Removal of two elements: 
[1, 2, 3, 4, 7, 8, 9, 10, 11, 12]

List after Removing a range of elements: 
[7, 8, 9, 10, 11, 12]

使用pop()方法

Pop()函数还可以用于从集合中移除和返回元素，但默认情况下，它只移除集合的最后一个元素。若要从列表的特定位置移除元素，元素的索引将作为参数传递给Pop()方法。

List = [1,2,3,4,5] 
  
# Removing element from the  
# Set using the pop() method 
List.pop() 
print("\nList after popping an element: ") 
print(List) 
  
# Removing element at a  
# specific location from the  
# Set using the pop() method 
List.pop(2) 
print("\nList after popping a specific element: ") 
print(List) 

输出：

List after popping an element: 
[1, 2, 3, 4]

List after popping a specific element: 
[1, 2, 4]

列表切片（Slicing of a List）

在Python List中，有多种方法可以打印包含所有元素的整个列表，但是要从列表中打印特定范围的元素，我们使用Slice操作。切片操作在使用冒号（：）的列表上执行。若要从开始到范围打印元素，请使用[：Index]；若要从结束使用[：-Index]打印元素；若要从特定索引打印元素，直到结束使用[Index:]；若要打印范围内的元素，请使用[开始索引：结束索引]；若要使用切片操作打印整个列表，请使用[：]。此外，要按相反顺序打印整个列表，请使用[：：-1]。

注意：要从后端打印列表元素，请使用负索引。

# Python program to demonstrate  
# Removal of elements in a List 
  
# Creating a List 
List = ['G','E','E','K','S','F', 
        'O','R','G','E','E','K','S'] 
print("Intial List: ") 
print(List) 
  
# Print elements of a range 
# using Slice operation 
Sliced_List = List[3:8] 
print("\nSlicing elements in a range 3-8: ") 
print(Sliced_List) 
  
# Print elements from a  
# pre-defined point to end 
Sliced_List = List[5:] 
print("\nElements sliced from 5th "
      "element till the end: ") 
print(Sliced_List) 
  
# Printing elements from 
# beginning till end 
Sliced_List = List[:] 
print("\nPrinting all elements using slice operation: ") 
print(Sliced_List) 

输出：

Intial List: 
['G', 'E', 'E', 'K', 'S', 'F', 'O', 'R', 'G', 'E', 'E', 'K', 'S']

Slicing elements in a range 3-8: 
['K', 'S', 'F', 'O', 'R']

Elements sliced from 5th element till the end: 
['F', 'O', 'R', 'G', 'E', 'E', 'K', 'S']

Printing all elements using slice operation: 
['G', 'E', 'E', 'K', 'S', 'F', 'O', 'R', 'G', 'E', 'E', 'K', 'S']

负索引列表切片

# Creating a List 
List = ['G','E','E','K','S','F', 
        'O','R','G','E','E','K','S'] 
print("Initial List: ") 
print(List) 
  
# Print elements from beginning 
# to a pre-defined point using Slice 
Sliced_List = List[:-6] 
print("\nElements sliced till 6th element from last: ") 
print(Sliced_List) 
  
# Print elements of a range 
# using negative index List slicing 
Sliced_List = List[-6:-1] 
print("\nElements sliced from index -6 to -1") 
print(Sliced_List) 
  
# Printing elements in reverse 
# using Slice operation 
Sliced_List = List[::-1] 
print("\nPrinting List in reverse: ") 
print(Sliced_List) 

输出：

Initial List: 
['G', 'E', 'E', 'K', 'S', 'F', 'O', 'R', 'G', 'E', 'E', 'K', 'S']

Elements sliced till 6th element from last: 
['G', 'E', 'E', 'K', 'S', 'F', 'O']

Elements sliced from index -6 to -1
['R', 'G', 'E', 'E', 'K']

Printing List in reverse: 
['S', 'K', 'E', 'E', 'G', 'R', 'O', 'F', 'S', 'K', 'E', 'E', 'G']

列表方法

带列表的内置函数