Python: List Comprehension

By Xah Lee. Date: . Last updated: .

What is List Comprehension

List Comprehension is a special syntax for building a list, or a nested list. You can use Python: Loop to do exactly the same, but List Comprehension makes the code shorter.

Syntax

List comprehension syntax has the form

[expression for var in list]

where expression is evaluated with var replaced by each element in list.

Example

# generate a list
xx = [i + 1 for i in [1, 2, 3]]
print(xx)
# [2, 3, 4]

Build a list of tuples:

# build a list of tuples
xx = [(i, i * 2) for i in range(1, 5)]
print(xx)
# [(1, 2), (2, 4), (3, 6), (4, 8)]

Nested Loop

xx = [(i, j) for i in range(2) for j in range(3)]
print(xx)
# [(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2)]