Python List Comprehensions Explained

What are List Comprehensions?

List comprehensions are a concise way to create lists in a single readable line, replacing multi-line for loops.

Before and After

# Traditional loop
squares = []
for n in range(5):
    squares.append(n ** 2)

# List comprehension — same result
squares = [n ** 2 for n in range(5)]
# [0, 1, 4, 9, 16]

Adding a Condition

evens = [n for n in range(10) if n % 2 == 0]
# [0, 2, 4, 6, 8]

The General Syntax

[expression for item in iterable if condition]

Dict and Set Comprehensions Too

squares = {n: n**2 for n in range(4)}   # dict
unique = {c for c in "hello"}            # set {'h','e','l','o'}

Real Example

users = [{"name": "Sara", "active": True}, {"name": "Ali", "active": False}]
active_names = [u["name"] for u in users if u["active"]]
# ['Sara']

FAQs

Are comprehensions faster than loops?

Usually slightly faster and always more readable for simple transforms. For complex logic, a regular loop is clearer.

Can I nest them?

Yes, but keep it readable. More in our Python section.