List comprehension is a compact way to create lists in Python. It replaces the traditional for loop with a single elegant line of code.

It improves readability, performance, and is widely used in data processing, filtering, and transformation.

Basic Syntax of List Comprehension

[expression for item in iterable if condition]

• expression: The item or operation to return
• item: Variable representing each element in the iterable
• iterable: A list, tuple, string, range, etc.
• condition: (optional) Filter to include specific items

1. Simple List Comprehension

Create a new list of items from another list.

Example:

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

Output:

['APPLE', 'BANANA', 'CHERRY']

2. Using if Condition

Filter items while creating the list.

Example:

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

Output:

[2, 4, 6]

3. With if...else in Expression

Add conditional logic to the output.

Example:

nums = [1, 2, 3, 4]
labels = ["Even" if n % 2 == 0 else "Odd" for n in nums]
print(labels)

Output:

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

4. Using range() and Math Operations

You can also perform calculations inside list comprehensions.

Example:

squares = [x**2 for x in range(6)]
print(squares)

Output:

[0, 1, 4, 9, 16, 25]

5. Nested List Comprehension

Used to flatten or process 2D lists.

Example: Flatten a matrix

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

Output:

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

6. Without Condition – Traditional vs Comprehension

Traditional for loop:

result = []
for x in range(5):
   result.append(x * 2)
print(result)

List comprehension:

result = [x * 2 for x in range(5)]
print(result)

Output (both):

[0, 2, 4, 6, 8]

Why Use List Comprehension?