In Python, the slicing operation allows you to obtain a subsequence from a sequence (such as a list, tuple, string, etc.) instead of the entire sequence. Slicing operations use colons (:) to specify the starting position, ending position, and step size.
The basic syntax for slicing is:
sequence[start:stop:step]
start: The index of the starting position (including the element at that position).stop: The index of the end position (excluding the element at that position).step: Step size, controls the interval of taking elements each time, the default value is 1.
Here are some common slicing operations:
- Get subsequence :
my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
subset = my_list[2:5] # 从索引2开始到索引5（不包括），结果为 [2, 3, 4]
- Specify step size :
my_string = "abcdefg"
subset = my_string[1:6:2] # 从索引1开始到索引6（不包括），步长为2，结果为 "bdf"
- Omit the start or end position :
my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
subset1 = my_list[:5] # 从开头到索引5（不包括），结果为 [0, 1, 2, 3, 4]
subset2 = my_list[5:] # 从索引5开始到结尾，结果为 [5, 6, 7, 8, 9]
- Reverse slicing :
my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
subset = my_list[::-1] # 从结尾到开头，步长为-1，实现反向，结果为 [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
- Modify elements in a slice :
my_list = [0, 1, 2, 3, 4, 5]
my_list[1:3] = [10, 20, 30] # 替换索引1到索引3（不包括）的元素，结果为 [0, 10, 20, 30, 3, 4, 5]
It should be noted that the slicing operation returns a new sequence, and the original sequence has not been changed.
Classic operations in slicing
- Forward slice to get elements
- Reverse slice to get elements
- Specify the step size to take elements
The meaning of slicing operation
Reduce the use of loops in your code