How to Slice Lists in Python

The Python programming language has support for lists, a list is a collection. It can be a collection of numbers, strings or other types of data.

The example below defines the list x:

x = [ 1,2,3,4,5,6,7,8 ]

How do you get only a part of the list?
You may think a for loop, which does the job, but there's an easier way.

Slice list

The Pythonic way is by defining brackets with start and ending position.
In between you write a colon, not a comma. Like this:

>>> x[1:3]

This looks similar to defining a list, but instead it takes a slice of the list.

This starts at the 2nd position (the element in Python is zero), and ends at the 4th position (3rd counting from zero). This may be a bit confusing initially.

>>> x = [1,2,3,4,5,6,7,8]
>>> x[1:3]
[2, 3]
>>> x[0:2]
[1, 2]
>>> x[0:3]
[1, 2, 3]
>>> 

If you want to start from the first character, you can leave the starting number out:

>>> x[:2]
[1, 2]
>>> x[:3]
[1, 2, 3]
>>> 

To create a new list, you can just do this:

>>> z = x[:2]
>>> z
[1, 2]
>>> 

You can use a list as an object, it supports function calls. This lets you sort the list, remove elements and more.

Related links:

• List in Python docs
• Learn Python

Comments

[Tomas Sheers]

In examples like this it might be clearer for your list to contain something like ["a", "b", "c", "d", ...] to avoid confusion with the index values used in the slicing