Python collections module
Python collections module
This is an extension of my 2025 Learning Log.
Python collections module contains specialized container datatypes that provide alternatives to Python’s general purpose built-in containers: dict, list, set, and tuple.
namedtuple
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from collections import namedtuple
FullName = namedtuple("FullName", ("first", "middle", "last"))
my_name = FullName("Barney", "The", "Dinosaur")
print(my_name[0]) # Barney
print(my_name.first) # Barney
print(my_name.first) = "Garfield" # AttributeError: can't set attribute
# namedtuples are read-only
deque
- lists with fixed maximum length (optional)
- double-sided limited lists
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from collections import deque
numbers = deque([], maxlen=5)
# first in, first out
for i in range(10):
numbers.append(i)
print(numbers)
"""
deque([0], maxlen=5)
deque([0, 1], maxlen=5)
deque([0, 1, 2], maxlen=5)
deque([0, 1, 2, 3], maxlen=5)
deque([0, 1, 2, 3, 4], maxlen=5)
deque([1, 2, 3, 4, 5], maxlen=5)
deque([2, 3, 4, 5, 6], maxlen=5)
deque([3, 4, 5, 6, 7], maxlen=5)
deque([4, 5, 6, 7, 8], maxlen=5)
deque([5, 6, 7, 8, 9], maxlen=5)
"""
numbers.appendleft(4)
print(numbers) # deque([4, 5, 6, 7, 8], maxlen=5)
n = numbers.popleft()
print(n) # 4
defaultdict
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from collections import defaultdict
# default element is an empty list
items = defaultdict(list)
items["Ethan"].append("views")
print(items) # defaultdict(<class 'list'>, {'Ethan': ['views']})
items = defaultdict(int)
items["Ethan"] += 1
print(items) # defaultdict(<class 'int'>, {'Ethan': 1})
items = defaultdict(lambda: 7)
items["Ethan"] += 1
print(items) # defaultdict(<function <lambda> at 0x103043d80>, {'Ethan': 8})
Counter
Counter - container that stores the elements as dictionary keys and their counts as dictionary values
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from collections import Counter
a = "aaaaabbbbccc"
my_counter = Counter(a)
print(my_counter) # Counter({'a': 5, 'b': 4, 'c': 3})
print(my_counter.most_common(1)) # [('a', 5)]
print(my_counter.most_common(2 # [('a', 5), ('b', 4)]
print(my_counter.most_common(1)[0][0]) # a
print(list(my_counter.elements())) # ['a', 'a', 'a', 'a', 'a', 'b', 'b', 'b', 'b', 'c', 'c', 'c']
OrderedDict
Remembers the order that the items were inserted. This is guaranteed already in Python 3.7 so OrderedDict are useful when using older Python versions
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from collections import OrderedDict
ordered_dict = OrderedDict()
ordered_dict["b"] = 2
ordered_dict["c"] = 3
ordered_dict["d"] = 4
ordered_dict["a"] = 1
print(ordered_dict) # OrderedDict({'b': 2, 'c': 3, 'd': 4, 'a': 1})
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