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Python List Comprehension: Learn with Examples

Python List Comprehension: In this tutorial, we will what is list comprehension and how to create a list using list comprehension with the help of examples. By Sapna Deraje Radhakrishna Last updated : June 15, 2023

Python List Comprehension

List comprehension is an important feature of Python, it provides shorter syntax to create a new list based on the existing list. List comprehension reduces the number of lines in list creation to a single line.

Syntax

The list comprehension starts with a [ and ], to ensure that the result is a list.

[expression for item in list]

The comprehension can also utilize the if condition.

Grouping elements using list comprehension

Group the common elements to a list: There are two lists with some elements, we have to create a list containing common elements.

Example

# Create two lists
grade_k = ['maddy', 'sriansh', 'owen', 'molly']
grade_first = ['molly', 'owen', 'ricky', 'sid']

# Print original lists
print("Original lists")
print("grade_k:", grade_k)
print("grade_first:", grade_first)

# Grouping common elements
common_names = [a for a in grade_k for b in grade_first if a == b]

# Print new list
print("Result (common_names):", common_names)

Output

Original lists
grade_k: ['maddy', 'sriansh', 'owen', 'molly']
grade_first: ['molly', 'owen', 'ricky', 'sid']
Result (common_names): ['owen', 'molly']

List of EVENs using list comprehension

List of EVEN numbers using list comprehension: Here, we will write a Python program that will create a list of EVEN numbers in a range.

Example

# List of EVEN numbers using 
# list comprehension
even_list = [n for n in range(30) if n % 2 == 0]

# Print list
print(even_list)

Output

[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28]

List by replacing specific elements using list comprehension

Here, we will write a program to create a new list by replacing all specific elements of an existing list.

Example

# list 1
list1 = ['molly', 'sriansh', 'owen', 'molly']

# print list 1
print("list1:", list1)

# New list by replacing 'molly' with 'alex
newlist = [v if v != 'molly' else 'alex' for v in list1]

# print new list
print("newlist:", newlist)

Output

list1: ['molly', 'sriansh', 'owen', 'molly']
newlist: ['alex', 'sriansh', 'owen', 'alex']

Nested List Comprehensions

Nested list comprehensions allow you to use list comprehension within the list comprehension.

Example

# Create a matrix using 
# nested list comprehension
mat = [[j for j in range(4)] for i in range(2)]

# Print list akka matrix
print(mat)

Output

[[0, 1, 2, 3], [0, 1, 2, 3]]

Advantages of using comprehension

1. Comprehensions requires less code. Python interpreter is optimized to run comprehensions as quickly as possible.
2. Comprehensions execute faster than for loop.
3. Comprehensions can be used in places where for loop cannot be used. All the comprehensions appear to the right of the assignment operator, which is something for loop cannot do.