Python Snippet

defaultdict for Implicit Init

Difficulty: Easy

`collections.defaultdict` removes the boilerplate of checking-then-initialising before every increment or append. It supplies a default value when a missing key is read, and that default lives in the dict from then on. This snippet covers the bucket-by-key pattern with `defaultdict(list)`, the count pattern with `defaultdict(int)`, and a nested `defaultdict` for two-level groupings.