collections.abc --- 容器的抽象基底類別

在 3.3 版被加入: 過去此模組是 collections 模組的一部分。

原始碼：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.

An issubclass() or isinstance() test for an interface works in one of three ways.

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
   

   Complex interfaces do not support this last technique because an interface is more than just the presence of method names. Interfaces specify semantics and relationships between methods that cannot be inferred solely from the presence of specific method names. For example, knowing that a class supplies __getitem__, __len__, and __iter__ is insufficient for distinguishing a Sequence from a Mapping.

在 3.9 版被加入: These abstract classes now support []. See 泛型別名型別 and PEP 585.

Collections Abstract Base Classes

The collections module offers the following ABCs:

ABC	Inherits from	抽象方法	Mixin Methods
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 和 count
MutableSequence	Sequence	__getitem__、__setitem__、__delitem__、__len__、insert	繼承 Sequence 方法和 append、clear、reverse、extend、pop、remove 和 __iadd__
ByteString	Sequence	__getitem__、__len__	Sequence 的繼承方法
Set	Collection	__contains__、__iter__、__len__	__le__、__lt__、__eq__、__ne__、__gt__、__ge__、__and__、__or__、__sub__、__rsub__、__xor__、__rxor__ 和 isdisjoint
MutableSet