Python | slice constructor
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Python's slice(~) constructor returns a slice object that usually contains a portion of a sequence.
Parameters
1. start | integer | optional
The start position for the slice object (inclusive). Defaults to 0.
2. stop | integer
The stop position for the slice object (non-inclusive).
3. step | integer | optional
Increment for each integer in the sequence. Defaults to 1.
Although we can use slice(start, stop, step) notation, the most common notation is indexing syntax sequence[start:stop:step].
Return value
A slice object that usually contains a portion of a sequence.
Examples
Basic usage
To create a slice object from start position 0 to stop position 5:
numbers = [0, 1, 2, 3, 4, 5]slice_object = slice(5)s1 = numbers[slice_object]s2 = numbers[:5]print(s1)print(s2)
[0, 1, 2, 3, 4][0, 1, 2, 3, 4]
We can see that both notation forms yield the same result.
Start parameter
To specify the start of the slice:
numbers = [0, 1, 2, 3, 4, 5]print(numbers[1:5])
[1, 2, 3, 4]
We can see that the resulting slice begins at value of index position 1 of numbers.
Step parameter
To specify the step of the slice:
numbers = [0, 1, 2, 3, 4, 5]print(numbers[1:6:2])
[1, 3, 5]
From start value of 1, we increment by 2 until we reach the stop value of 6.
Negative Index
To specify negative start, stop and step:
letters = ('S', 'k', 'y', 'T', 'o', 'w', 'n', 'e', 'r')print(letters[-1:-5:-1])
('r', 'e', 'n', 'w')
By specifying start of -1 we start at the last element of the tuple, ad a step of -1 means we work backwards by one index position increment at a time until index position -5 (fifth to last element in original tuple).
