How to Get the Number of Elements in a Python List?

Problem Formulation: Given a list of elements in Python. How to get the number of elements in the list?

Examples:

Method 1: len()

The most Pythonic way to get the number of list elements is Python’s built-in function len() that returns the length of the list, regardless of its elements’ types.

>>> len([])
0
>>> len([3, 42, 2])
3
>>> len(['Alice', 'Bob', 'Carl'])
3
>>> len([(1, 2), [3, 4]])
2

You can dive into Python’s built-in len() function in more detail in my video tutorial:

You can also use the len() function to determine the number of elements in a Python list, tuple, string, dictionary, and set.

Related Tutorial: Python len()

Method 2: len() + set() to Count the Number of Unique Elements

To count the number of unique list elements, you can combine Python’s built-in functions len() and set() to obtain len(set(list)). This converts the list to a set and removes all duplicates. The length of the duplicate-free set is the number of unique elements in the original list.

Here’s an example:

>>> lst = [1, 2, 3, 1, 1, 1]
>>> len(lst)
6
>>> len(set(lst))
3

Method 3: How to Get the Number of Elements in a Nested List?

A nested list is a list that contains other lists that may can contain other lists and so on. To get the number of elements in a nested list, you can flatten the list and pass the flattened list into the len() function.

Here’s the code:

>>> from pandas.core.common import flatten
>>> lst = [[1, 2], [3, [4, 5, 6]], [4]]
>>> list(flatten(lst))
[1, 2, 3, 4, 5, 6, 4]
>>> len(list(flatten(lst)))
7

Note that there are many more ways to flatten a list of lists. You can read about them in our full tutorial.

Related Tutorial: Flatten A List Of Lists In Python