Can list be modified in python?

The elements of the list are equivalent to variables, so the program can assign values ​​to the elements of the list, so that the elements of the list can be modified. For example, the following code:

a_list = [2, 4, -3.4, 'crazyit', 23]# 对第3个元素赋值
a_list[2] = 'fkit'print(a_list) # [2, 4, 'fkit', 'crazyit', 23]
# 对倒数第2个元素赋值
a_list[-2] = 9527
print(a_list) # [2, 4, 'fkit', 9527, 23]

The above code assigns values ​​to list elements through indexes. The program can use either positive indexes or negative indexes, and there is no problem.

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In addition, the program can also assign values ​​to part of the list through slice syntax. When performing this operation, the number of newly assigned elements is not required. The number is equal to the original number of elements.
This means that elements can be added to the list or deleted from the list in this way. For example, the following code demonstrates assigning a value to a segment in the middle of the list:

b_list = list(range(1, 5))
print(b_list)# 将第2个到第4个（不包含）元素赋值为新列表的元素
b_list[1: 3] = ['a', 'b']
print(b_list) # [1, 'a', 'b', 4]

If you assign a value to an empty slice in the list, it becomes inserting elements into the list. For example, the following code:

# 将第3个到第3个（不包含）元素赋值为新列表的元素，就是插入
b_list[2: 2] = ['x', 'y']
print(b_list) # [1, 'a', 'x', 'y', 'b', 4]

If you assign a section of the list to an empty list, it becomes deleting elements from the list. For example, the following code:

# 将第3个到第6个（不包含）元素赋值为空列表，就是删除
b_list[2: 5] = []
print(b_list) # [1, 'a', 4]

When using slice syntax to assign values ​​to a list, you cannot use a single value; if you use string assignment, Python will automatically treat the string as a sequence, in which each character is a element. For example, the following code:

# Python会自动将str分解成序列
b_list[1: 3] = 'Charlie'
print(b_list) # [1, 'C', 'h', 'a', 'r', 'l', 'i', 'e']

When using the slice syntax to assign values, you can also specify the step parameter. However, if the step parameter is specified, the number of list elements assigned is required to be equal to the number of list elements replaced. For example, the following code:

c_list = list(range(1, 10))
# 指定step为2，被赋值的元素有4个，因此用于赋值的列表也必须有4个元素
c_list[2: 9: 2] = ['a', 'b', 'c', 'd']
print(c_list) # [1, 2, 'a', 4, 'b', 6, 'c', 8, 'd']

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