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# Python | slice constructor

schedule Aug 12, 2023
Last updated
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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`.

NOTE

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).

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