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

Added in version 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`.

Added in version 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__`, `__rsub__`, `__xor__`, `__rxor__` 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` |  | `__init__`, `__len__` and `__repr__`
`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__`
`Buffer` [1] |  | `__buffer__` |

Виноски

[1] (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15)

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.

  See Annotating callable objects for details on how to use `Callable` in type annotations.

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.

  Added in version 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.

  Added in version 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.

  See Annotating generators and coroutines for details on using `Generator` in type annotations.

  Added in version 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.

  index(value, start=0, stop=None)

    Return first index of value.

    Raises `ValueError` if the value is not present.

    Supporting the start and stop arguments is optional, but recommended.

    Змінено в версії 3.5: The `index()` method gained support for the stop and start arguments.

  Deprecated since version 3.12, will be removed in version 3.17: The `ByteString` ABC has been deprecated.

  Use `isinstance(obj, collections.abc.Buffer)` to test if `obj` implements the buffer protocol at runtime. For use in type annotations, either use `Buffer` or a union that explicitly specifies the types your code supports (e.g., `bytes | bytearray | memoryview`).

  `ByteString` was originally intended to be an abstract class that would serve as a supertype of both `bytes` and `bytearray`. However, since the ABC never had any methods, knowing that an object was an instance of `ByteString` never actually told you anything useful about the object. Other common buffer types such as `memoryview` were also never understood as subtypes of `ByteString` (either at runtime or by static type checkers).

  See PEP 688 for more details.

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.

  Added in version 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.

  See Annotating generators and coroutines for details on using `Coroutine` in type annotations. The variance and order of type parameters correspond to those of `Generator`.

  Added in version 3.5.

class collections.abc.AsyncIterable

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

  Added in version 3.5.

class collections.abc.AsyncIterator

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

  Added in version 3.5.

class collections.abc.AsyncGenerator

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

  See Annotating generators and coroutines for details on using `AsyncGenerator` in type annotations.

  Added in version 3.6.

class collections.abc.Buffer

  ABC for classes that provide the `__buffer__()` method, implementing the buffer protocol. See PEP 688.

  Added in version 3.12.

## 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.