Note that the list comprehension can also be constructed by considering the set-builder construction for the same example:
{n2 | n ∈ Z ∧ 0 ≤ n ≤ 9 }.
While a full understanding of set-builder notation is not necessary for working with list comprehensions, in some instances they may lead to a more natural translation to list comprehensions than equivalent loop-based code.
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python3:list_comprehensions
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Table of Contents
List Comprehensions
List comprehensions are used for creating lists from existing lists and other iterable structures. List comprehensions typically follow formatting similar to set-builder notation in discrete mathematics.
Syntax
Consider the following illustrative Python3 example for generating a list of squares:
>>> sq = [] >>> for i in range(10): ... sq.append(i**2) ... >>> sq [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
The same could be achieved in the following list comprehension1)
>>> [i**2 for i in range(10)] [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
Multiple Loops
Note that this basic syntax is easily extended to multiple loops and variables:
>>> [(x**2, y**2) for x in range(3) for y in range(3)] [(0, 0), (0, 1), (0, 4), (1, 0), (1, 1), (1, 4), (4, 0), (4, 1), (4, 4)]
python3/list_comprehensions.1557254965.txt.gz · Last modified: 2019/05/07 13:49 by jguerin
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