Lists and Tuples in Python

Lists and Tuples in Python

by John Sturtz basics python
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Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Lists and Tuples in Python

Lists and tuples are arguably Python’s most versatile, useful data types. You will find them in virtually every nontrivial Python program.

Here’s what you’ll learn in this tutorial: You’ll cover the important characteristics of lists and tuples. You’ll learn how to define them and how to manipulate them. When you’re finished, you should have a good feel for when and how to use these object types in a Python program.

Python Lists

In short, a list is a collection of arbitrary objects, somewhat akin to an array in many other programming languages but more flexible. Lists are defined in Python by enclosing a comma-separated sequence of objects in square brackets ([]), as shown below:

Python 
>>> a = ['foo', 'bar', 'baz', 'qux']

>>> print(a)
['foo', 'bar', 'baz', 'qux']
>>> a
['foo', 'bar', 'baz', 'qux']

The important characteristics of Python lists are as follows:

  • Lists are ordered.
  • Lists can contain any arbitrary objects.
  • List elements can be accessed by index.
  • Lists can be nested to arbitrary depth.
  • Lists are mutable.
  • Lists are dynamic.

Each of these features is examined in more detail below.

Lists Are Ordered

A list is not merely a collection of objects. It is an ordered collection of objects. The order in which you specify the elements when you define a list is an innate characteristic of that list and is maintained for that list’s lifetime. (You will see a Python data type that is not ordered in the next tutorial on dictionaries.)

Lists that have the same elements in a different order are not the same:

Python 
>>> a = ['foo', 'bar', 'baz', 'qux']
>>> b = ['baz', 'qux', 'bar', 'foo']
>>> a == b
False
>>> a is b
False

>>> [1, 2, 3, 4] == [4, 1, 3, 2]
False

Lists Can Contain Arbitrary Objects

A list can contain any assortment of objects. The elements of a list can all be the same type:

Python 
>>> a = [2, 4, 6, 8]
>>> a
[2, 4, 6, 8]

Or the elements can be of varying types:

Python 
>>> a = [21.42, 'foobar', 3, 4, 'bark', False, 3.14159]
>>> a
[21.42, 'foobar', 3, 4, 'bark', False, 3.14159]

Lists can even contain complex objects, like functions, classes, and modules, which you will learn about in upcoming tutorials:

Python 
>>> int
<class 'int'>
>>> len
<built-in function len>
>>> def foo():
...     pass
...
>>> foo
<function foo at 0x035B9030>
>>> import math
>>> math
<module 'math' (built-in)>

>>> a = [int, len, foo, math]
>>> a
[<class 'int'>, <built-in function len>, <function foo at 0x02CA2618>,
<module 'math' (built-in)>]

A list can contain any number of objects, from zero to as many as your computer’s memory will allow:

Python 
>>> a = []
>>> a
[]

>>> a = [ 'foo' ]
>>> a
['foo']

>>> a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
... 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
... 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55