List comprehension is a concise and powerful way to create lists in Python. It allows you to generate, transform, and filter list items using a single line of code.

Compared to traditional for loops, list comprehensions are often shorter, more readable, and easier to write.

What is List Comprehension?

List comprehension creates a new list by applying an expression to each item in an iterable.

Syntax

[expression for item in iterable]
            

Example

numbers = [1, 2, 3, 4, 5] 
squares = [num ** 2 for num in numbers] 
print(squares)
            

Output:

[1, 4, 9, 16, 25]
            

Creating a List Using a Loop

Without list comprehension:

numbers = [1, 2, 3, 4, 5] 
squares = [] 
for num in numbers: 
    squares.append(num ** 2) 
print(squares)
            

Output:

[1, 4, 9, 16, 25]
            

Using list comprehension produces the same result with less code.

List Comprehension with Conditions

You can add an if condition to include only specific items.

Syntax

[expression for item in iterable if condition]
            

Example

numbers = [1, 2, 3, 4, 5, 6] 
even_numbers = [num for num in numbers if num % 2 == 0] print(even_numbers)
            

Output:

[2, 4, 6]
            

Only even numbers are included in the new list.

Creating a List of Strings

Example

fruits = ["apple", "banana", "mango"] 
uppercase_fruits = [fruit.upper() for fruit in fruits] print(uppercase_fruits)
            

Output:

['APPLE', 'BANANA', 'MANGO']
            

Using range() with List Comprehension

Example

numbers = [x for x in range(1, 6)] print(numbers)
            

Output:

[1, 2, 3, 4, 5]
            

Using an if-else Condition

You can use conditional expressions inside list comprehensions.

Syntax

[expression_if_true if condition else expression_if_false for item in iterable]
            

Example

numbers = [1, 2, 3, 4, 5] 
result = ["Even" if num % 2 == 0 else "Odd" for num in numbers] print(result)
            

Output:

['Odd', 'Even', 'Odd', 'Even', 'Odd']
            

List Comprehension with Strings

Example

word = "Python" letters = [letter for letter in word] print(letters)
            

Output:

['P', 'y', 't', 'h', 'o', 'n']
            

Nested List Comprehension

List comprehensions can also be nested.

Example

matrix = [[1, 2], [3, 4], [5, 6]] 
flattened = [item for row in matrix for item in row] 
print(flattened)
            

Output:

[1, 2, 3, 4, 5, 6]
            

Benefits of List Comprehension

• Reduces the amount of code.
• Improves readability for simple operations.
• Often performs faster than equivalent for loops.
• Makes data transformation easier.