`slice()`

The built-in slice() function creates a slice object representing a set of indices specified by range(start, stop, step). This object can be used to extract portions of sequences like strings, lists, or tuples:

>>> numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> even_numbers = numbers[slice(1, None, 2)]
>>> even_numbers
[2, 4, 6, 8]

`slice()` Signatures

slice(stop, /)
slice(start, stop, step=None, /)

Arguments

Argument	Description	Default Value
`start`	The initial index of the slice.	`None` (start of the sequence)
`stop`	The ending index of the slice, exclusive.	Required argument
`step`	The step between each index in the slice.	`None` (step of `1`)

Return Value

Returns a slice object that can be used to extract a portion of a sequence.

Since Python 3.12, slice objects are hashable, provided that start, stop, and step are hashable, so they can be dictionary keys or set members.

`slice()` Examples

With only a stop value:

>>> letters = ["A", "B", "C", "D", "E"]
>>> letters[slice(3)]
['A', 'B', 'C']

With start, stop, and step values:

>>> numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> numbers[slice(1, 8, 2)]
[1, 3, 5, 7]

`slice()` Common Use Cases

The most common use cases for the slice() function include:

Extracting a subset of elements from a sequence.
Creating copies of sequences.

`slice()` Real-World Example

Say that you have a list of daily temperatures and want to extract only the temperatures for the first day of each week, skipping weekends:

>>> temperatures = [20, 21, 19, 22, 18, 17, 23, 24, 25, 26, 22, 21, 19, 20]
>>> weekdays = temperatures[slice(0, None, 7)]
>>> weekdays
[20, 24]

In this example, slice(0, None, 7) allows you to select every 7th temperature starting from the first element, effectively picking temperatures for the first day of each week.

Tutorial

Reverse Strings in Python: reversed(), Slicing, and More

In this step-by-step tutorial, you'll learn how to reverse strings in Python by using available tools such as reversed() and slicing operations. You'll also learn about a few useful ways to build reversed strings by hand.

basics best-practices python

For additional information on related topics, take a look at the following resources: