# `collections.abc` — Abstract Base Classes for Containers

Нове в версії 3.3: Раніше цей модуль був частиною модуля `collections`.

Вихідний код: Lib/_collections_abc.py

This module provides abstract base classes that can be used to test whether a class provides a particular interface; for example, whether it is hashable or whether it is a mapping.

Тест `issubclass()` або `isinstance()` для інтерфейсу працює одним із трьох способів.

1) A newly written class can inherit directly from one of the abstract base classes. The class must supply the required abstract methods. The remaining mixin methods come from inheritance and can be overridden if desired. Other methods may be added as needed:

    class C(Sequence):                      # Direct inheritance
        def __init__(self): ...             # Extra method not required by the ABC
        def __getitem__(self, index):  ...  # Required abstract method
        def __len__(self):  ...             # Required abstract method
        def count(self, value): ...         # Optionally override a mixin method

    >>> issubclass(C, Sequence)
    True
    >>> isinstance(C(), Sequence)
    True

2) Existing classes and built-in classes can be registered as «virtual subclasses» of the ABCs. Those classes should define the full API including all of the abstract methods and all of the mixin methods. This lets users rely on `issubclass()` or `isinstance()` tests to determine whether the full interface is supported. The exception to this rule is for methods that are automatically inferred from the rest of the API:

    class D:                                 # No inheritance
        def __init__(self): ...              # Extra method not required by the ABC
        def __getitem__(self, index):  ...   # Abstract method
        def __len__(self):  ...              # Abstract method
        def count(self, value): ...          # Mixin method
        def index(self, value): ...          # Mixin method

    Sequence.register(D)                     # Register instead of inherit

    >>> issubclass(D, Sequence)
    True
    >>> isinstance(D(), Sequence)
    True

In this example, class `D` does not need to define `__contains__`, `__iter__`, and `__reversed__` because the in-operator, the iteration logic, and the `reversed()` function automatically fall back to using `__getitem__` and `__len__`.

3) Some simple interfaces are directly recognizable by the presence of the required methods (unless those methods have been set to `None`):

    class E:
        def __iter__(self): ...
        def __next__(self): ...

    >>> issubclass(E, Iterable)
    True
    >>> isinstance(E(), Iterable)
    True

Складні інтерфейси не підтримують цю останню техніку, оскільки інтерфейс — це більше, ніж просто наявність назв методів. Інтерфейси визначають семантику та зв’язки між методами, які не можуть бути виведені лише з наявності конкретних імен методів. Наприклад, відомості про те, що клас надає `__getitem__`, `__len__` і `__iter__`, недостатньо для того, щоб відрізнити `Sequence` від `Mapping`.

Нове в версії 3.9: Ці абстрактні класи тепер підтримують `[]`. Див. Загальний тип псевдоніма і PEP 585.

## Колекції Абстрактні базові класи

Модуль колекцій пропонує наступне ABCs:

ABC | Успадковує від | Методи реферату | Методи Міксіна
--- | --- | --- | ---
`Container` [1] |  | `__contains__` |
`Hashable` [1] |  | `__hash__` |
`Iterable` [1] [2] |  | `__iter__` |
`Iterator` [1] | `Iterable` | `__next__` | `__iter__`
`Reversible` [1] | `Iterable` | `__reversed__` |
`Generator` [1] | `Iterator` | `відправити`, `кинути` | `закрити`, `__iter__`, `__next__`
`Sized` [1] |  | `__len__` |
`Callable` [1] |  | `__call__` |
`Collection` [1] | `Sized`, `Iterable`, `Container` | `__contains__`, `__iter__`, `__len__` |
`Sequence` | `Reversible`, `Collection` | `__getitem__`, `__len__` | `__contains__`, `__iter__`, `__reversed__`, `index` і `count`
`MutableSequence` | `Sequence` | `__getitem__`, `__setitem__`, `__delitem__`, `__len__`, `вставити` | Inherited `Sequence` methods and `append`, `clear`, `reverse`, `extend`, `pop`, `remove`, and `__iadd__`
`ByteString` | `Sequence` | `__getitem__`, `__len__` | Успадковані методи `Sequence`
`Set` | `Collection` | `__contains__`, `__iter__`, `__len__` | `__le__`, `__lt__`, `__eq__`, `__ne__`, `__gt__`, `__ge__`, `__and__`, `__or__`, `__sub__`, `__xor__`, and `isdisjoint`
`MutableSet` | `Set` | `__contains__`, `__iter__`, `__len__`, `add`, `discard` | Успадковані методи `Set` і `clear`, `pop`, `remove`, `__ior__`, `__iand__`, `__ixor__` та `__isub__`
`Mapping` | `Collection` | `__getitem__`, `__iter__`, `__len__` | `__contains__`, `keys`, `items`, `values`, `get`, `__eq__` і `__ne__`
`MutableMapping` | `Mapping` | `__getitem__`, `__setitem__`, `__delitem__`, `__iter__`, `__len__` | Успадковані методи `Mapping` і `pop`, `popitem`, `clear`, `update` і `setdefault`
`MappingView` | `Sized` |  | `__len__`
`ItemsView` | `MappingView`, `Set` |  | `__contains__`, `__iter__`
`KeysView` | `MappingView`, `Set` |  | `__contains__`, `__iter__`
`ValuesView` | `MappingView`, `Collection` |  | `__contains__`, `__iter__`
`Awaitable` [1] |  | `__await__` |
`Coroutine` [1] | `Awaitable` | `відправити`, `кинути` | `закрити`
`AsyncIterable` [1] |  | `__aiter__` |
`AsyncIterator` [1] | `AsyncIterable` | `__anext__` | `__aiter__`
`AsyncGenerator` [1] | `AsyncIterator` | `asend`, `athrow` | `aclose`, `__aiter__`, `__anext__`

Виноски

[1] (1,2,3,4,5,6,7,8,9,10,11,12,13,14)

These ABCs override `__subclasshook__()` to support testing an interface by verifying the required methods are present and have not been set to `None`. This only works for simple interfaces. More complex interfaces require registration or direct subclassing.

[ 2 ]

Checking `isinstance(obj, Iterable)` detects classes that are registered as `Iterable` or that have an `__iter__()` method, but it does not detect classes that iterate with the `__getitem__()` method. The only reliable way to determine whether an object is iterable is to call `iter(obj)`.

## Колекції абстрактних базових класів – докладні описи

class collections.abc.Container

  ABC for classes that provide the `__contains__()` method.

class collections.abc.Hashable

  ABC for classes that provide the `__hash__()` method.

class collections.abc.Sized

  ABC for classes that provide the `__len__()` method.

class collections.abc.Callable

  ABC for classes that provide the `__call__()` method.

class collections.abc.Iterable

  ABC for classes that provide the `__iter__()` method.

  Checking `isinstance(obj, Iterable)` detects classes that are registered as `Iterable` or that have an `__iter__()` method, but it does not detect classes that iterate with the `__getitem__()` method. The only reliable way to determine whether an object is iterable is to call `iter(obj)`.

class collections.abc.Collection

  ABC для класів ітерованих контейнерів розміру.

  Нове в версії 3.6.

class collections.abc.Iterator

  ABC для класів, які забезпечують методи `__iter__()` і `__next__()`. Дивіться також визначення iterator.

class collections.abc.Reversible

  ABC for iterable classes that also provide the `__reversed__()` method.

  Нове в версії 3.6.

class collections.abc.Generator

  ABC for generator classes that implement the protocol defined in PEP 342 that extends iterators with the `send()`, `throw()` and `close()` methods.

  Нове в версії 3.5.

class collections.abc.Sequence
class collections.abc.MutableSequence
class collections.abc.ByteString

  Азбука для доступних лише для читання та змінних послідовностей.

  Implementation note: Some of the mixin methods, such as `__iter__()`, `__reversed__()` and `index()`, make repeated calls to the underlying `__getitem__()` method. Consequently, if `__getitem__()` is implemented with constant access speed, the mixin methods will have linear performance; however, if the underlying method is linear (as it would be with a linked list), the mixins will have quadratic performance and will likely need to be overridden.

  Змінено в версії 3.5: Метод index() додав підтримку аргументів stop і start.

class collections.abc.Set
class collections.abc.MutableSet

  ABCs for read-only and mutable sets.

class collections.abc.Mapping
class collections.abc.MutableMapping

  Азбука лише для читання та змінних відображення.

class collections.abc.MappingView
class collections.abc.ItemsView
class collections.abc.KeysView
class collections.abc.ValuesView

  Азбука зіставлення, елементів, ключів і значень views.

class collections.abc.Awaitable

  ABC for awaitable objects, which can be used in `await` expressions. Custom implementations must provide the `__await__()` method.

  Coroutine об’єкти та екземпляри `Coroutine` ABC є екземплярами цього ABC.

  Примітка

  In CPython, generator-based coroutines (generators decorated with `@types.coroutine`) are awaitables, even though they do not have an `__await__()` method. Using `isinstance(gencoro, Awaitable)` for them will return `False`. Use `inspect.isawaitable()` to detect them.

  Нове в версії 3.5.

class collections.abc.Coroutine

  ABC for coroutine compatible classes. These implement the following methods, defined in Об’єкти співпрограми: `send()`, `throw()`, and `close()`. Custom implementations must also implement `__await__()`. All `Coroutine` instances are also instances of `Awaitable`.

  Примітка

  In CPython, generator-based coroutines (generators decorated with `@types.coroutine`) are awaitables, even though they do not have an `__await__()` method. Using `isinstance(gencoro, Coroutine)` for them will return `False`. Use `inspect.isawaitable()` to detect them.

  Нове в версії 3.5.

class collections.abc.AsyncIterable

  ABC for classes that provide an `__aiter__` method. See also the definition of asynchronous iterable.

  Нове в версії 3.5.

class collections.abc.AsyncIterator

  ABC для класів, які надають методи `__aiter__` і `__anext__`. Дивіться також визначення asynchronous iterator.

  Нове в версії 3.5.

class collections.abc.AsyncGenerator

  ABC for asynchronous generator classes that implement the protocol defined in PEP 525 and PEP 492.

  Нове в версії 3.6.

## Приклади та рецепти

ABC дозволяє нам запитувати класи чи екземпляри, чи надають вони певну функціональність, наприклад:

    size = None
    if isinstance(myvar, collections.abc.Sized):
        size = len(myvar)

Several of the ABCs are also useful as mixins that make it easier to develop classes supporting container APIs. For example, to write a class supporting the full `Set` API, it is only necessary to supply the three underlying abstract methods: `__contains__()`, `__iter__()`, and `__len__()`. The ABC supplies the remaining methods such as `__and__()` and `isdisjoint()`:

    class ListBasedSet(collections.abc.Set):
        ''' Alternate set implementation favoring space over speed
            and not requiring the set elements to be hashable. '''
        def __init__(self, iterable):
            self.elements = lst = []
            for value in iterable:
                if value not in lst:
                    lst.append(value)

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

        def __contains__(self, value):
            return value in self.elements

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

    s1 = ListBasedSet('abcdef')
    s2 = ListBasedSet('defghi')
    overlap = s1 & s2            # The __and__() method is supported automatically

Примітки щодо використання `Set` і `MutableSet` як міксину:

1. Since some set operations create new sets, the default mixin methods need a way to create new instances from an iterable. The class constructor is assumed to have a signature in the form `ClassName(iterable)`. That assumption is factored-out to an internal `classmethod` called `_from_iterable()` which calls `cls(iterable)` to produce a new set. If the `Set` mixin is being used in a class with a different constructor signature, you will need to override `_from_iterable()` with a classmethod or regular method that can construct new instances from an iterable argument.

2. To override the comparisons (presumably for speed, as the semantics are fixed), redefine `__le__()` and `__ge__()`, then the other operations will automatically follow suit.

3. The `Set` mixin provides a `_hash()` method to compute a hash value for the set; however, `__hash__()` is not defined because not all sets are hashable or immutable. To add set hashability using mixins, inherit from both `Set()` and `Hashable()`, then define `__hash__ = Set._hash`.

Дивись також

- Рецепт OrderedSet для прикладу, побудованого на `MutableSet`.

- Щоб дізнатися більше про ABC, перегляньте модуль `abc` і PEP 3119.