Py Collections Module — Free Python Tutorial
Learn Py Collections Module in Python with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.
TL;DR: Learn Py Collections Module in Python with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
Py Collections Module in Python
The collections module provides specialised container types that extend Python's built-in dict, list, and tuple for common patterns — more efficient and expressive than implementing them yourself.
Counter(iterable) counts hashable elements and stores them as {element: count}. It supports arithmetic (+, -, &, |) and most_common(n) returns the n highest-count elements.
defaultdict(default_factory) is a dict that never raises KeyError — it calls default_factory() to create a missing value on first access. Common factories: list, set, int (for counting without Counter).
deque (double-ended queue) supports O(1) append/pop from BOTH ends, unlike list which is O(n) for left-side operations. Use maxlen for a sliding window or fixed-size history buffer.
Other highlights: OrderedDict (remembers insertion order — mostly superseded by dict in Python 3.7+), namedtuple (lightweight class-like tuple with field names), ChainMap (logical merge of multiple dicts).
Py Collections Module — Syntax
from collections import Counter, defaultdict, deque, namedtuple
Counter("banana") # Counter({'a':3,'n':2,'b':1})
Counter.most_common(2) # [('a',3),('n',2)]
dd = defaultdict(list)
dd["key"].append(1) # no KeyError
dq = deque([1,2,3], maxlen=3)
dq.appendleft(0) # O(1)! deque → [0,1,2]
Point = namedtuple("Point", ["x","y"])
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