Python List Comprehension: The Complete Guide (2026)

What are list comprehensions? List comprehensions are one of Python's most distinctive features -- a concise, readable syntax for creating lists by transforming and filtering elements from existing iterables. They replace multi-line for loop patterns with a single expression that is both easier to read and faster to execute. The basic syntax looks like this: new_list = [expression for item in iterable] This is equivalent to the following for loop: new_list = [] for item in iterable: new_list.append(expression) The difference is not just cosmetic. List comprehensions are optimized at the bytecode level. Python's compiler recognizes the pattern and uses a specialized LIST_APPEND opcode instead of the repeated attribute lookup and method call that list.append() requires. This is why list comprehensions are consistently faster than their for loop equivalents, as we will demonstrate with benchmarks later in this guide. A brief history List comprehensions were introduced in Python 2.0 throug