Collections

The built-in list, dict, set, and tuple cover most needs, but the standard-library collections module adds a handful of specialised containers that make common jobs shorter, clearer, and often faster. Counting things, grouping things, working efficiently at both ends of a sequence, giving tuple fields names — each has a purpose-built type that turns several lines of fiddly code into one obvious one.

This guide covers the five you'll actually reach for — Counter, defaultdict, deque, namedtuple, and the pair OrderedDict/ChainMap — and, just as importantly, when each is the right tool over a plain dict or list.

Sections

• Learn — four notebooks: counting with Counter, grouping with defaultdict, fast double-ended sequences with deque, and named records with namedtuple (plus OrderedDict and ChainMap).
• Recipes — counting and tallying, grouping items by a key, building queues and sliding windows, and the mistakes these containers invite.
• Reference — Counter/defaultdict, deque, and namedtuple/OrderedDict/ChainMap lookups.
• Concepts — essays on why specialised containers exist at all, and how to choose the right one.

New to the topic? Start with Learn → Counter. Here for a specific task? Recipes is task-focused and Reference is for lookups. This guide builds directly on Data structures.