collections — Specialized Data Structures

Counter — count occurrences:

from collections import Counter

words = ["apple", "banana", "apple", "cherry", "banana", "apple"]
count = Counter(words)
count["apple"]          # 3
count.most_common(2)    # [("apple", 3), ("banana", 2)]

defaultdict — dict with default values:

from collections import defaultdict

graph = defaultdict(list)
graph["A"].append("B")  # No KeyError even if "A" didn't exist

word_count = defaultdict(int)
for word in words:
    word_count[word] += 1  # No KeyError for new keys

deque — double-ended queue:

from collections import deque

q = deque([1, 2, 3])
q.appendleft(0)   # add to front
q.append(4)       # add to back
q.popleft()       # remove from front (O(1) vs list O(n))

namedtuple — tuple with named fields:

from collections import namedtuple
Point = namedtuple("Point", ["x", "y"])
p = Point(3, 4)
p.x  # 3
p.y  # 4

Reference:

Wikipedia: Python

https://en.wikipedia.org/wiki/Python_(programming_language)