Use slicing to retrieve a subsequence from a Python sequence such as a string, list, or tuple. In `sequence[start:stop]`, the start is included and the stop is excluded. section 4.1
Omit the start to begin at the first item, or omit the stop to continue through the end. Add a step to select items at intervals; a negative step processes the sequence from right to left, so use it with care. Although out-of-range slice indices are tolerated, avoid relying on them when they make the intended bounds unclear. section 4.1.1 section 4.1.5
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9] assert numbers[2:5:2] == [3, 5] #1 assert numbers[::3] == [1, 4, 7] #2 assert numbers[::-1] == [9, 8, 7, 6, 5, 4, 3, 2, 1] #3
These list examples show stepped selection, an omitted start and stop, and reversal. section 4.1.1
A slice object, created with `slice(start, stop, step)`, can be reused to select subsequences. Unlike a `range`, it is not iterable; use ranges for iteration and slices as sequence subscripts. Named slices can clarify repeated selections. Slicing also supports replacing, expanding, shrinking, or removing subsequences in mutable sequences such as lists and bytearrays. section 4.1.2 section 4.1.5 section 4.6
