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

Νέο στην έκδοση 3.3: Παλαιότερα, αυτό το module ήταν μέρος του `collections` module.

Πηγαίος κώδικας: 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.

Ένας έλεγχος `issubclass()` ή `isinstance()` για μια διεπαφή λειτουργεί με έναν από τρεις τρόπους.

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__(next): ...

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

Οι σύνθετες διεπαφές δεν υποστηρίζουν αυτή την τελευταία τεχνική επειδή μια διεπαφή είναι κάτι περισσότερο από την παρουσία ονομάτων μεθόδων. Οι διεπαφές καθορίζουν τη σημασιολογία και τις σχέσεις μεταξύ των μεθόδων που δεν μπορούν να συναχθούν αποκλειστικά από την παρουσία συγκεκριμένων ονομάτων μεθόδων. Για παράδειγμα, η γνώση ότι μια κλάση παρέχει τις μεθόδους `__getitem__`, `__len__` και `__iter__` δεν είναι επαρκής για να διακρίνει μια κλάση `Sequence` από μια κλάση `Mapping`.

Νέο στην έκδοση 3.9: Αυτές οι αφηρημένες κλάσεις υποστηρίζουν πλέον `[]`. Δείτε Τύπος Generic Alias και PEP 585.

## Αφηρημένες Βασικές Κλάσεις Συλλογών

Το collections module προσφέρει τις εξής ABCs:

ABC | Κληρονομεί από | Αφηρημένες Μέθοδοι | Mixin Μέθοδοι
--- | --- | --- | ---
`Container` 1 |  | `__contains__` |
`Hashable` 1 |  | `__hash__` |
`Iterable` 1 2 |  | `__iter__` |
`Iterator` 1 | `Iterable` | `__next__` | `__iter__`
`Reversible` 1 | `Iterable` | `__reversed__` |
`Generator` 1 | `Iterator` | `send`, `throw` | `close`, `__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`, and `count`
`MutableSequence` | `Sequence` | `__getitem__`, `__setitem__`, `__delitem__`, `__len__`, `insert` | Inherited `Sequence` methods and `append`, `reverse`, `extend`, `pop`, `remove`, and `__iadd__`
`ByteString` | `Sequence` | `__getitem__`, `__len__` | Κληρονομημένες `Sequence` μέθοδοι
`Set` | `Collection` | `__contains__`, `__iter__`, `__len__` | `__le__`, `__lt__`, `__eq__`, `__ne__`, `__gt__`, `__ge__`, `__and__`, `__or__`, `__sub__`, `__xor__`, and `isdisjoint`
`MutableSet` | `Set` | `__contains__`, `__iter__`, `__len__`, `add`, `discard` | Κληρονομημένες `Set` μέθοδοι και `clear`, `pop`, `remove`, `__ior__`, `__iand__`, `__ixor__`, και `__isub__`
`Mapping` | `Collection` | `__getitem__`, `__iter__`, `__len__` | `__contains__`, `keys`, `items`, `values`, `get`, `__eq__`, και `__ne__`
`MutableMapping` | `Mapping` | `__getitem__`, `__setitem__`, `__delitem__`, `__iter__`, `__len__` | Κληρονομημένες `Mapping` μέθοδοι και `pop`, `popitem`, `clear`, `update`, και `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` | `send`, `throw` | `close`
`AsyncIterable` 1 |  | `__aiter__` |
`AsyncIterator` 1 | `AsyncIterable` | `__anext__` | `__aiter__`
`AsyncGenerator` 1 | `AsyncIterator` | `asend`, `athrow` | `aclose`, `__aiter__`, `__anext__`

Υποσημειώσεις

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

  These ABCs override `object.__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)`.

## Αφηρημένες Βασικές Κλάσεις Συλλογών – Αναλυτικές Περιγραφές

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 για τις κλάσεις επαναλαμβανόμενων container με μέγεθος.

  Νέο στην έκδοση 3.6.

class `collections.abc.``Iterator`

  ABC για κλάσεις που παρέχουν τις μεθόδους `__iter__()` και `__next__()`. Δείτε επίσης τον ορισμό του iterator.

class `collections.abc.``Reversible`

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

  Νέο στην έκδοση 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 also the definition of generator.

  Νέο στην έκδοση 3.5.

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

  ABCs μόνο για ανάγνωση (read-only) και mutable sequences.

  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.

  Άλλαξε στην έκδοση 3.5: Η μέθοδος index() πρόσθεσε υποστήριξη για τα ορίσματα stop και start.

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

  ABCs for read-only and mutable sets.

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

  ABCs μόνο για ανάγνωση (read-only) και mutable mappings.

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

  ABCs για αντιστοιχήσεις, στοιχεία, κλειδιά και τιμές views.

class `collections.abc.``Awaitable`

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

  Τα αντικείμενα Coroutine και τα στιγμιότυπα της κλάσης `Coroutine` είναι όλα παραδείγματα αυτής της ABC.

  Σημείωση

  In CPython, generator-based coroutines (generators decorated with `types.coroutine()` or `asyncio.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.

  Νέο στην έκδοση 3.5.

class `collections.abc.``Coroutine`

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

  Σημείωση

  In CPython, generator-based coroutines (generators decorated with `types.coroutine()` or `asyncio.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.

  Νέο στην έκδοση 3.5.

class `collections.abc.``AsyncIterable`

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

  Νέο στην έκδοση 3.5.

class `collections.abc.``AsyncIterator`

  ABC για κλάσεις που παρέχουν τις μεθόδους `__aiter__` και `__anext__`. Δείτε επίσης τον ορισμό του asynchronous iterator.

  Νέο στην έκδοση 3.5.

class `collections.abc.``AsyncGenerator`

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

  Νέο στην έκδοση 3.6.

## Παραδείγματα και Συνταγές

Οι ABCs επιτρέπουν να ρωτήσουμε τις κλάσεις ή τα αντικείμενα αν παρέχουν συγκεκριμένη λειτουργικότητα, για παράδειγμα:

    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

Σημειώσεις για τη χρήση των `Set` και `MutableSet` ως mixin:

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`.

Δείτε επίσης

- Συνταγή OrderedSet για ένα παράδειγμα που βασίζεται στην κλάση `MutableSet`.

- Για περισσότερα σχετικά με τις ABCs, δείτε το `abc` module και το PEP 3119.