List Comprehensions

This lesson covers list comprehensions, a distinctly Python way to build a list in a single line without an explicit for loop. It's written for anyone searching "Python list comprehension tutorial".

A list comprehension is a Python idiom that builds a list without a for loop, all on one line. Written as [expression for variable in list if condition], it lets you gather only the elements matching a condition, or transform each element. It can feel a little hard to read at first, but once you're used to it, it expresses the same intent far more concisely than a multi-line for loop.

The sample code uses [n for n in nums if n % 2 == 0] to gather only the even numbers, and [n ** 2 for n in nums] to build a list of each element squared. Writing the same logic with a regular for loop would require creating an empty list first and calling .append() repeatedly — the comprehension expresses that in a single line.

A common beginner mistake is cramming too much logic into a comprehension, making it harder to read rather than easier. If a comprehension gets too dense, it becomes counterproductive — don't hesitate to fall back to a regular for loop once conditions or nesting start piling up.

List comprehensions are one of Python's signature, most-loved idioms, and they show up constantly in real code — preprocessing data for analysis, reshaping an API response, and more. Getting comfortable reading and writing them will also make it much faster to understand other people's Python code.