Python collections.abc Module

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In this guide, you'll explore Python's collections.abc module, which defines abstract base classes for containers. Learn its features and examples for better code design.

The collections.abc module in Python provides abstract base classes (ABCs) for various container types, allowing you to define and check for container interfaces. These ABCs are useful for type checking and ensuring that custom container types implement the necessary methods to behave like standard containers.

Table of Contents

1. Introduction
2. Container ABCs
   • Container
   • Hashable
   • Iterable
   • Iterator
   • Generator
   • Sized
   • Callable
   • Collection
   • Sequence
   • MutableSequence
   • ByteString
   • Set
   • MutableSet
   • Mapping
   • MutableMapping
   • MappingView
   • KeysView
   • ItemsView
   • ValuesView
3. Examples
   • Checking for Interface Compliance
   • Creating a Custom Iterable
   • Implementing a Custom Mutable Mapping
4. Real-World Use Case
5. Conclusion
6. References

Introduction

The collections.abc module provides a set of abstract base classes that define the fundamental interfaces for container types in Python. These interfaces ensure that custom container types provide the necessary methods to work seamlessly with the rest of Python's data model. By inheriting from these ABCs, you can create custom containers that are compatible with Python's standard containers.

Container ABCs

Container

The Container class checks if an object supports the in operator.

from collections.abc import Container

class MyContainer:
    def __contains__(self, item):
        return item in self.items

container = MyContainer()
print(isinstance(container, Container))

Output:

True

Hashable

The Hashable class checks if an object supports hashing.

from collections.abc import Hashable

print(isinstance(42, Hashable))
print(isinstance([], Hashable))

Output:

True
False

Iterable

The Iterable class checks if an object supports iteration.

from collections.abc import Iterable

print(isinstance([], Iterable))
print(isinstance({}, Iterable))

Output:

True
True

Iterator

The Iterator class checks if an object supports iteration and the __next__ method.

from collections.abc import Iterator

it = iter([1, 2, 3])
print(isinstance(it, Iterator))

Output:

True

Generator

The Generator class checks if an object is a generator.

from collections.abc import Generator

def gen():
    yield 1

g = gen()
print(isinstance(g, Generator))

Output:

True

Sized

The Sized class checks if an object has a __len__ method.

from collections.abc import Sized

print(isinstance([], Sized))
print(isinstance({}, Sized))

Output:

True
True

Callable

The Callable class checks if an object is callable.

from collections.abc import Callable

print(isinstance(lambda x: x, Callable))

Output:

True

Collection

The Collection class is a base class for collections that are iterable, sized, and container.

from collections.abc import Collection

print(isinstance([], Collection))
print(isinstance({}, Collection))

Output:

True
True

Sequence

The Sequence class checks if an object supports sequence operations like indexing and slicing.

from collections.abc import Sequence

print(isinstance([], Sequence))
print(isinstance({}, Sequence))

Output:

True
False

MutableSequence

The MutableSequence class checks if an object supports mutable sequence operations.

from collections.abc import MutableSequence

print(isinstance([], MutableSequence))

Output:

True

ByteString

The ByteString class checks if an object supports byte string operations.

from collections.abc import ByteString

print(isinstance(b'abc', ByteString))

Output:

C:\Users\rames\AppData\Local\Temp\script16814326250219225151.py:3: DeprecationWarning: 'collections.abc.ByteString' is deprecated and slated for removal in Python 3.14
  print(isinstance(b'abc', ByteString))
True

Set

The Set class checks if an object supports set operations.

from collections.abc import Set

print(isinstance(set(), Set))

Output:

True

MutableSet

The MutableSet class checks if an object supports mutable set operations.

from collections.abc import MutableSet

print(isinstance(set(), MutableSet))

Output:

True

Mapping

The Mapping class checks if an object supports mapping (dictionary-like) operations.

from collections.abc import Mapping

print(isinstance({}, Mapping))

Output:

True

MutableMapping

The MutableMapping class checks if an object supports mutable mapping operations.

from collections.abc import MutableMapping

print(isinstance({}, MutableMapping))

Output:

True

MappingView

The MappingView class checks if an object supports mapping view operations.

KeysView

The KeysView class checks if an object supports keys view operations.

ItemsView

The ItemsView class checks if an object supports items view operations.

ValuesView

The ValuesView class checks if an object supports values view operations.

Examples

Checking for Interface Compliance

Check if a custom container class conforms to the Sequence interface.

from collections.abc import Sequence

class MyList:
    def __getitem__(self, index):
        return index

    def __len__(self):
        return 10

my_list = MyList()
print(isinstance(my_list, Sequence))

Output:

False

Creating a Custom Iterable

Create a custom iterable class.

from collections.abc import Iterable

class MyIterable(Iterable):
    def __iter__(self):
        yield from [1, 2, 3]

my_iterable = MyIterable()
for item in my_iterable:
    print(item)

Output:

1
2
3

Implementing a Custom Mutable Mapping

Create a custom mutable mapping class.

from collections.abc import MutableMapping

class MyDict(MutableMapping):
    def __init__(self):
        self.store = dict()

    def __getitem__(self, key):
        return self.store[key]

    def __setitem__(self, key, value):
        self.store[key] = value

    def __delitem__(self, key):
        del self.store[key]

    def __iter__(self):
        return iter(self.store)

    def __len__(self):
        return len(self.store)

my_dict = MyDict()
my_dict['a'] = 1
my_dict['b'] = 2
print(my_dict['a'])
print(my_dict)

Output:

1
<__main__.MyDict object at 0x0000021902E165A0>

Real-World Use Case

Validating Data Structures

Suppose you are writing a function that processes various data structures. You can use the collections.abc module to validate that the input conforms to the expected interfaces.

from collections.abc import Mapping, Sequence

def process_data(data):
    if isinstance(data, Mapping):
        print("Processing mapping data")
        for key, value in data.items():
            print(f"{key}: {value}")
    elif isinstance(data, Sequence):
        print("Processing sequence data")
        for item in data:
            print(item)
    else:
        raise TypeError("Unsupported data type")

process_data({'a': 1, 'b': 2})
process_data([1, 2, 3])

Output:

Processing mapping data
a: 1
b: 2
Processing sequence data
1
2
3

Conclusion

The collections.abc module in Python provides a robust framework for defining and working with container interfaces. By leveraging these abstract base classes, you can ensure that your custom container types are fully compatible with Python's data model, making your code more flexible and interoperable.

References

• Python collections.abc module documentation