all Python 3collectionsterm

collections

module

Specialised containers: Counter, defaultdict, deque, namedtuple, OrderedDict and ChainMap.

Syntax

import collections

It covers tasks where built-in list and dict are awkward: counting (Counter), default values (defaultdict), a queue with fast ends (deque). Abstract container interfaces live in the collections.abc submodule, and typed records are easier with dataclasses. A common mistake is a queue built on list with pop(0): that is O(n), while deque.popleft is O(1).

Examples

from collections import Counter, defaultdict, deque
print(Counter('abracadabra').most_common(1))  # → [('a', 5)]
groups = defaultdict(list)
groups['x'].append(1)
print(dict(groups))  # → {'x': [1]}
print(deque([1, 2, 3], maxlen=2))  # → deque([2, 3], maxlen=2)

See also

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