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Find size of a list in Python

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  • Difficulty Level : Basic
  • Last Updated : 12 Nov, 2018

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




# 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))

Output:

The length of list is:  4

Example 2:




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

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

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