What does x[::] mean in python?

Slicing is a way to get values ​​from a list. The value is taken from the beginning to the end. Note: The step size of slicing defaults to 1 and cannot be 0

For example: (Recommended learning: Python video tutorial)

num2 = [1, 2, 3, 4, 5, ["a", "b", "c", ["d", "e"]]]
print(num2[3:6]) # 这个切片表示获取从第三个元素到第六个元素的值，当前列表中只有5个元素，由于切片的性质顾头不顾尾，所以要取的最后一个值，就必须是6
>>>[4, 5, ['a', 'b', 'c', ['d', 'e']]]
print(num2[:3])#从头开始取，取到第二个元素
>>>[1, 2, 3]
print(num2[1:5:2]) #取 索引为1 到 4的值，步长为2
# print(num2[::2]) #表示取所有的值，步长为2

print(num2[::-1])#切片步长为负数，从后面往前面取值，相当于翻转了
>>>[['a', 'b', 'c', ['d', 'e']], 5, 4, 3, 2, 1]

Note: The step size is a negative number, If the front is a positive number, it will be empty when taken out

print(num2[1:5:-1])

>>>[]

# 切片的操作适用于字符串，但是字符串的值不能修改
#注：list 是可变的；字符串和元组是不可变的

Change (reassign)

names_class2=['张三','李四','王五','赵六'] 
names_class2[3]='赵七'
names_class2[0:2]=['wusir','alvin'] 
print(names_class2)

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