Are list comprehensions faster than for-loops?

Usually yes, because they avoid repeated attribute lookups for list.append and run in optimized C code internally.

Python List Comprehension: A Practical Guide

Published April 2, 2026·Updated October 29, 2026·6 min read

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Introduction

List comprehensions let you build lists in a single readable line instead of a multi-line for-loop. This guide covers the syntax, common patterns, and when to avoid them.

Prerequisites

Basic Python syntax
Familiarity with for-loops

Step-by-Step Guide

Step 1: Basic syntax

A list comprehension has the form [expression for item in iterable].

squares = [n * n for n in range(10)]

Step 2: Adding a condition

Filter items with an if clause at the end of the comprehension.

evens = [n for n in range(20) if n % 2 == 0]

Step 3: Nested comprehensions

Flatten a matrix by nesting two for clauses in the same comprehension.

flat = [n for row in matrix for n in row]

FAQs

Are list comprehensions faster than for-loops?: Usually yes, because they avoid repeated attribute lookups for list.append and run in optimized C code internally.

Summary

List comprehensions are a core Python idiom. Use them for simple transformations and filters, but fall back to a regular loop when logic gets complex.

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