Find size of a list in Python

In Python, List is a collection data-type which is ordered and changeable. A list can have duplicate entry as well. Here, the task is find the number of entries in a list. See the examples below.

Examples:

Input : a = [1, 2, 3, 1, 2, 3]
Output : 6
Count the number of entries in the list a.

Input : a = []
Output : 0

The idea is to use len() in Python

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python program to demonstrate working
# of len()
a = []
a.append("Hello")
a.append("Geeks")
a.append("For")
a.append("Geeks")
print("The length of list is: ", len(a))

chevron_right


Output:

The length of list is:  4

Example 2:



filter_none

edit
close

play_arrow

link
brightness_4
code

# Python program to demonstrate working
# of len()
n = len([10, 20, 30])
print("The length of list is: ", n)

chevron_right


Output:

The length of list is:  3

How does len() work?
len() works in O(1) time as list is an object and has a member to store its size. Below is description of len() from Python docs.

Return the length (the number of items) of an object. The argument may be a sequence (such as a string, bytes, tuple, list, or range) or a collection (such as a dictionary, set, or frozen set).

How to check if a list is empty in Python

Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course.

My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.