Comprehensions

A comprehension is a concise notation for performing some operation on each element of a collection of objects, and/or selecting a subset of elements that satisfy some condition. They are borrowed from the functional programming language Haskell (https://www.haskell.org/) and, together with iterators and generators, contribute to giving Python a functional flavor.

Python offers different types of comprehensions: list, dictionary, and set. We'll concentrate mainly on list comprehensions; once you understand those, the other types will be quite easy to grasp.

Let's start with a very simple example. We want to calculate a list with the squares of the first 10 natural numbers. How would you do it? There are a couple of equivalent ways:

# squares.map.py
# If you code like this you are not a Python dev! ;)
>>> squares = []
>>> for n in range(10):
...     squares.append(n ** 2)
...
>>> squares
[0, 1, 4, 9, 16, 25, 36, 49...