Python 列表就像动态大小的数组，用其他语言声明（C++ 中的向量和 Java 中的 ArrayList）。用简单的语言来说，列表就是事物的集合，用 [ ] 括起来并用逗号分隔。
列表是一种序列数据类型，用于存储数据集合。元组和字符串是其他类型的序列数据类型。
这里我们使用 [] 创建 Python列表。
Var = ["Geeks", "for", "Geeks"] print(Var)
输出：
["Geeks", "for", "Geeks"]
列表是最简单的容器，是 Python 语言不可或缺的一部分。列表不必总是同质的，这使它成为Python中最强大的工具。单个列表可能包含数据类型，如整数、字符串和对象。列表是可变的，因此即使在创建之后也可以更改。
Python 中的列表可以通过将序列放在方括号 [] 内来创建。与Sets不同，列表不需要内置函数来创建列表。
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("Blank List: ") print(List) # Creating a List of numbers List = [10, 20, 14] print("\nList of numbers: ") print(List) # Creating a List of strings and accessing # using index List = ["Geeks", "For", "Geeks"] print("\nList Items: ") print(List[0]) print(List[2])
输出
Blank List: [] List of numbers: [10, 20, 14] List Items: Geeks Geeks
时间复杂度： O(1)
空间复杂度： O(n)
列表可能包含具有不同位置的重复值，因此，多个不同或重复的值可以在创建列表时作为序列传递。
# 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)
使用数字列表： [1, 2, 4, 4, 3, 3, 3, 6, 5] 使用混合值列表： [1, 2, 'Geeks', 4, 'For', 6 , '极客']
要访问列表项，请参考索引号。使用索引运算符 [ ] 访问列表中的项目。索引必须是整数。使用嵌套索引访问嵌套列表。
示例 1：访问列表中的元素
# 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])
Accessing a element from the list Geeks Geeks
示例 2：访问多维列表中的元素
# Creating a Multi-Dimensional List # (By Nesting a list inside a List) List = [['Geeks', 'For'], ['Geeks']] # accessing an element from the # Multi-Dimensional List using # index number print("Accessing a element from a Multi-Dimensional list") print(List[0][1]) print(List[1][0])
Accessing a element from a Multi-Dimensional list For Geeks
在 Python 中，负序索引表示从数组末尾开始的位置。不必像 List[len(List)-3] 那样计算偏移量，只写 List[-3] 就足够了。负索引表示从末尾开始，-1 表示最后一项，-2 表示倒数第二项，依此类推。
List = [1, 2, 'Geeks', 4, 'For', 6, 'Geeks'] # accessing an element using # negative indexing print("Accessing element using negative indexing") # print the last element of list print(List[-1]) # print the third last element of list print(List[-3])
Accessing element using negative indexing Geeks For
空间复杂度： O(1)
Python len()用于获取列表的长度。
# Creating a List List1 = [] print(len(List1)) # Creating a List of numbers List2 = [10, 20, 14] print(len(List2))
0 3
我们可以将元素列表的输入作为字符串、整数、浮点数等。但默认的是字符串。
示例 1：
# Python program to take space # separated input as a string # split and store it to a list # and print the string list # input the list as string string = input("Enter elements (Space-Separated): ") # split the strings and store it to a list lst = string.split() print('The list is:', lst) # printing the list
Enter elements: GEEKS FOR GEEKS The list is: ['GEEKS', 'FOR', 'GEEKS']
示例 2：
# input size of the list n = int(input("Enter the size of list : ")) # store integers in a list using map, # split and strip functions lst = list(map(int, input("Enter the integer\ elements:").strip().split()))[:n] # printing the list print('The list is:', lst)
Enter the size of list : 4 Enter the integer elements: 6 3 9 10 The list is: [6, 3, 9, 10]
可以使用内置的append()函数将元素添加到列表中。使用 append() 方法一次只能将一个元素添加到列表中，对于使用 append() 方法添加多个元素，使用循环。也可以使用 append 方法将元组添加到列表中，因为元组是不可变的。与集合不同，列表也可以使用 append() 方法添加到现有列表中。
# 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)
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']]
append() 方法仅适用于在 List 末尾添加元素，要在所需位置添加元素，使用insert()方法。与仅接受一个参数的 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)
Initial List: [1, 2, 3, 4] List after performing Insert Operation: ['Geeks', 1, 2, 3, 12, 4]
时间复杂度： O(n)
除了 append() 和 insert() 方法之外，还有一种添加元素的方法，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)
Initial List: [1, 2, 3, 4] List after performing Extend Operation: [1, 2, 3, 4, 8, 'Geeks', 'Always']
可以使用Python 中的 reverse() 方法反转列表。
# Reversing a list mylist = [1, 2, 3, 4, 5, 'Geek', 'Python'] mylist.reverse() print(mylist)
['Python', 'Geek', 5, 4, 3, 2, 1]
可以使用内置的remove()函数从列表中删除元素，但如果列表中不存在该元素，则会出现错误。Remove() 方法一次只删除一个元素，要删除一系列元素，使用迭代器。remove() 方法删除指定的项目。
注意： List 中的 Remove 方法只会删除第一次出现的搜索元素。
# 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("Initial 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)
Initial 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]
# Creating a List List = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] # 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)
List after Removing a range of elements: [5, 6, 7, 8, 9, 10, 11, 12]
pop() 函数也可用于从列表中移除和返回一个元素，但默认情况下它只移除列表的最后一个元素，从列表的特定位置移除元素，传递元素的索引作为 pop() 方法的参数。
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)
List after popping an element: [1, 2, 3, 4] List after popping a specific element: [1, 2, 4]
时间复杂度： O(1)/O(n)（O(1) 删除最后一个元素，O(n) 删除第一个和中间元素）
我们可以使用切片获取子字符串和子列表。在 Python List 中，有多种方法可以打印包含所有元素的整个列表，但是要打印列表中特定范围的元素，我们使用 Slice操作。
使用冒号（:）对列表执行切片操作。
要打印从开始到范围的元素，请使用：
[: Index]
从最终用途打印元素：
打印特定索引中的元素直到最终使用
[:-Index]
要以相反的顺序打印整个列表，请使用
[::-1]
注意 –要从后端打印 List 的元素，请使用负索引。
理解列表的切片：
# 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("Initial 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)
Initial 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']
# 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)
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']
Python 列表推导式用于从其他可迭代对象（如元组、字符串、数组、列表等）创建新列表。列表推导式由包含表达式的括号组成，该表达式针对每个元素以及 for 循环执行以迭代每个元素。
句法：
newList = [ expression(element) for element in oldList if condition ]
例子：
# Python program to demonstrate list # comprehension in Python # below list contains square of all # odd numbers from range 1 to 10 odd_square = [x ** 2 for x in range(1, 11) if x % 2 == 1] print(odd_square)
[1, 9, 25, 49, 81]
为了更好的理解，上面的代码类似如下：
# for understanding, above generation is same as, odd_square = [] for x in range(1, 11): if x % 2 == 1: odd_square.append(x**2) print(odd_square)
原文链接：codingdict.net
