👪 The Collections Module¶

The collections module is a very useful built-in Python module that implements specialized container data types, providing alternatives to Python’s general purpose built-in containers.

1. Counter¶

Counter is a dict subclass for counting objects:

In [2]:

from collections import Counter

colors = ['blue', 'red', 'blue', 'green', 'red', 'blue']
counter = Counter(colors)

print(counter)  # Outputs: Counter({'blue': 3, 'red': 2, 'green': 1})

from collections import Counter colors = ['blue', 'red', 'blue', 'green', 'red', 'blue'] counter = Counter(colors) print(counter) # Outputs: Counter({'blue': 3, 'red': 2, 'green': 1})

Counter({'blue': 3, 'red': 2, 'green': 1})

2. defaultdict¶

defaultdict is a dict subclass that calls a factory function to supply missing values:

In [3]:

from collections import defaultdict

color_counts = defaultdict(int)
colors = ['blue', 'red', 'blue', 'green', 'red', 'blue']

for color in colors:
    color_counts[color] += 1

print(color_counts)  # Outputs: defaultdict(<class 'int'>, {'blue': 3, 'red': 2, 'green': 1})

from collections import defaultdict color_counts = defaultdict(int) colors = ['blue', 'red', 'blue', 'green', 'red', 'blue'] for color in colors: color_counts[color] += 1 print(color_counts) # Outputs: defaultdict(, {'blue': 3, 'red': 2, 'green': 1})

defaultdict(<class 'int'>, {'blue': 3, 'red': 2, 'green': 1})

3. OrderedDict¶

An OrderedDict is a dict subclass that remembers the order entries were added:

In [4]:

from collections import OrderedDict

favorite_colors = OrderedDict()
favorite_colors['Tom'] = 'blue'
favorite_colors['Anna'] = 'red'
favorite_colors['John'] = 'green'

for name, color in favorite_colors.items():
    print(f"{name}'s favorite color is {color}")

from collections import OrderedDict favorite_colors = OrderedDict() favorite_colors['Tom'] = 'blue' favorite_colors['Anna'] = 'red' favorite_colors['John'] = 'green' for name, color in favorite_colors.items(): print(f"{name}'s favorite color is {color}")

Tom's favorite color is blue
Anna's favorite color is red
John's favorite color is green

4. namedtuple¶

namedtuple generates a subclass of tuple that has named fields, an alternative to namedtuple is the dataclass decorator, which is available in Python 3.7 and newer.

In [5]:

from collections import namedtuple

# Define a new tuple subclass named 'Color'
Color = namedtuple('Color', ['red', 'green', 'blue'])

color = Color(blue=55, green=155, red=255)
print(color.red)  # Outputs: 255

from collections import namedtuple # Define a new tuple subclass named 'Color' Color = namedtuple('Color', ['red', 'green', 'blue']) color = Color(blue=55, green=155, red=255) print(color.red) # Outputs: 255

255

5. deque¶

deque is a list-like container with fast appends and pops on either end:

In [6]:

from collections import deque

# Create a deque
d = deque('ghi')  # make a new deque with three items
for elem in d:  # iterate over the deque's elements
    print(elem.upper())

from collections import deque # Create a deque d = deque('ghi') # make a new deque with three items for elem in d: # iterate over the deque's elements print(elem.upper())

G
H
I

The collections module is very useful for a variety of tasks and can make your code cleaner and faster.