Counter, defaultdict, namedtuple

The collections module saves you boilerplate.

Counter

A dict subclass that counts hashable items. .most_common(n) is the killer feature.

defaultdict

A dict where missing keys auto-create a default value. defaultdict(list) is the cleanest way to group things.

namedtuple

A tuple with named fields. Tiny, fast, and lets you write p.x instead of p[0]. Modern alternative: dataclasses.dataclass (we'll meet it later).

Try it

1. Use Counter to find the 3 most-common letters in "abracadabra".
2. Use defaultdict(int) to count votes from ["a","b","a","c","b","a"].