Lesson 19 — functools.reduce

Fold a sequence

reduce(fn, items) collapses a list into one value. It calls fn with the first two items, then calls fn again with that result and the next item, and so on to the end. You can pass a start value as a third argument.

from functools import reduce
print(reduce(lambda a, b: a if a > b else b, [3, 9, 4]))  # 9

Why it matters: it expresses running products, totals and merges in one line.