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

In this article, we will discuss how we get the number of elements in a Python list.

Example

Input: [1,2,3,4,5]
Output: 5
Explanation: No of elements in the list are 5

Input: [1.2 ,4.5, 2.2]  
Output: 3
Explanation: No of elements in the list are 3 

Input: [“apple”, “banana”, “mangoe”]
Output: 3
Explanation: No of elements in the list are 3

Before getting the count of items in the Python List, we have to create an empty List and store some items in the List.

Methods to Get the Number of Elements in the List

• Using Python len( ) function
• Using for loop 
• Using operator length_hint function
• Using Numpy Library

Using Len() function to Get the Number of Elements

We can use the len( ) function to return the number of elements present in the list. To efficiently count items in a list, you can use Python’s built-in functions.

Python3

elem_list = [1, 2, 3, 4]
print(elem_list)
print("No of elements in list are:", len(elem_list))

Output:

[1, 2, 3, 4]
No of elements in list are: 4

Time Complexity: O(1)
Auxiliary Space: O(1)

Using for loop Get the Number of Elements

We can declare a counter variable to count the number of elements in the list using a for loop and print the counter after the loop in Python gets terminated. In this way we get number of items in a list.

Python3

item_list = [1, 2, 3, 4]
count = 0
for i in item_list:

    count = count+1


print(item_list)
print("No of elements in the list are:", count)

Output:

[1, 2, 3, 4]
No of elements in the list are: 4

Time Complexity: O(n) 
Auxiliary Space: O(1)

Using length_hint Get the Number of Elements in a List

In this example we are using the length_hint() function to get number of items in a list.

Python3

from operator import length_hint

l = [1, 2, 3, 4]
print(length_hint(l))

Output:

4

Time Complexity: O(1) 
Auxiliary Space: O(1)

Counting elements Using Numpy Library

This code uses the NumPy library to count the number of elements in a Python list named elem_list, which contains the elements [1, 2, 3, 4]. The code prints the list and then outputs the message “No of elements in list are: 4,” indicating that there are four elements in the list.

Python3

import numpy as np
elem_list = [1, 2, 3, 4]
print(elem_list)
print("No of elements in list are:", np.size(elem_list))

Output:

[1, 2, 3, 4]
No of elements in list are: 4

Time Complexity: O(n), where n is the number of elements in the list
Auxiliary Space: O(1)

Get Number of Unique Elements in a List

To get the number of unique elements in a list, we can use the set data structure in Python.

In this code, my_list contains duplicate elements. By converting it to a set, we eliminate duplicates, and then we calculate the length of the set to get the count of unique elements.

Python3

my_list = [1, 2, 2, 3, 4, 4, 5]
unique_elements = set(my_list)
count_unique = len(unique_elements)

print("Original List:", my_list)
print("Number of Unique Elements:", count_unique)

Output

Original List: [1, 2, 2, 3, 4, 4, 5]
Number of Unique Elements: 5

Get Total Number of Elements in a List Containing Other Lists

To get the total number of elements in a list that contains other lists, you can use recursion to traverse all the nested lists and count their elements. In this way we count items in list.

This code defines a count_total_elements function that recursively iterates through the list and its sublists. It counts the elements and returns the total count. The example nested_list demonstrates the function’s usage.

Python3

def count_total_elements(my_list):
    total_elements = 0

    for item in my_list:
        if isinstance(item, list):
            total_elements += count_total_elements(item)
        else:
            total_elements += 1

    return total_elements

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

total_elements = count_total_elements(nested_list)

print("Nested List:", nested_list)
print("Total Number of Elements:", total_elements)

Output

Nested List: [1, [2, 3, [4, 5]], [6, 7], 8]
Total Number of Elements: 8