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collections ​

The collections module is a built-in module in Python that provides various specialized container classes.

namedtuple ​

A namedtuple allows you to create tuple-like objects with named fields, improving code readability. For example, a point in 2D space can be represented as:

python
from collections import namedtuple
Point = namedtuple('Point', ['x', 'y'])
p = Point(1, 2)
print(p.x)  # 1
print(p.y)  # 2

This makes it easy to define custom data types that maintain tuple immutability while allowing attribute access.

deque ​

A deque (double-ended queue) is an optimized list for fast appends and pops from both ends:

python
from collections import deque
q = deque(['a', 'b', 'c'])
q.append('x')         # Add to the right
q.appendleft('y')     # Add to the left
print(q)  # deque(['y', 'a', 'b', 'c', 'x'])

defaultdict ​

A defaultdict returns a default value when a key does not exist, eliminating the need for key existence checks:

python
from collections import defaultdict
dd = defaultdict(lambda: 'N/A')
dd['key1'] = 'abc'
print(dd['key1'])  # 'abc'
print(dd['key2'])  # 'N/A'

OrderedDict ​

An OrderedDict maintains the order of keys based on insertion:

python
from collections import OrderedDict
od = OrderedDict([('a', 1), ('b', 2), ('c', 3)])
print(od)  # OrderedDict([('a', 1), ('b', 2), ('c', 3)])

This is particularly useful for preserving the order of elements when iterating.

ChainMap ​

ChainMap links multiple dictionaries, providing a single view of them. It’s useful for parameter lookup with priority:

python
from collections import ChainMap
import os, argparse

defaults = {'color': 'red', 'user': 'guest'}
parser = argparse.ArgumentParser()
parser.add_argument('-u', '--user')
parser.add_argument('-c', '--color')
namespace = parser.parse_args()
command_line_args = {k: v for k, v in vars(namespace).items() if v}

combined = ChainMap(command_line_args, os.environ, defaults)
print('color=%s' % combined['color'])
print('user=%s' % combined['user'])

Counter ​

A Counter is a subclass of dict designed for counting hashable objects:

python
from collections import Counter
c = Counter('programming')
print(c)  # Counter({'g': 2, 'r': 2, 'm': 2, ...})
c.update('hello')  # Update with new data
print(c)

Summary ​

The collections module provides various specialized container classes that enhance Python's built-in types, allowing for more efficient and readable data manipulation.