"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"、  | "__contains__"、        |                                                      |
|                                | "Container"            | "__iter__"、"__len__"   |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Sequence"                     | "Reversible",          | "__getitem__"、         | "__contains__"、"__iter__"、"__reversed__"、"index"  |
|                                | "Collection"           | "__len__"               | 和 "count"                                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableSequence"              | "Sequence"             | "__getitem__"、         | 繼承 "Sequence" 方法和 "append"、"clear"、"reverse"  |
|                                |                        | "__setitem__"、         | 、"extend"、"pop"、 "remove" 和 "__iadd__"           |
|                                |                        | "__delitem__"、         |                                                      |
|                                |                        | "__len__"、"insert"     |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "ByteString"                   | "Sequence"             | "__getitem__"、         | "Sequence" 的繼承方法                                |
|                                |                        | "__len__"               |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Set"                          | "Collection"           | "__contains__"、        | "__le__"、"__lt__"、"__eq__"、"__ne__"、"__gt__"、   |
|                                |                        | "__iter__"、"__len__"   | "__ge__"、"__and__" 、"__or__"、"__sub__"、          |
|                                |                        |                         | "__rsub__"、"__xor__"、"__rxor__" 和 "isdisjoint"    |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableSet"                   | "Set"                  | "__contains__"、        | Inherited "Set" methods and "clear", "pop",          |
|                                |                        | "__iter__"、"__len__"、 | "remove", "__ior__", "__iand__", "__ixor__", and     |
|                                |                        | "add"、"discard"        | "__isub__"                                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Mapping"                      | "Collection"           | "__getitem__"、         | "__contains__"、"keys"、"items"、"values"、"get"、   |
|                                |                        | "__iter__"、"__len__"   | "__eq__" 和 "__ne__"                                 |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableMapping"               | "Mapping"              | "__getitem__"、         | Inherited "Mapping" methods and "pop", "popitem",    |
|                                |                        | "__setitem__"、         | "clear", "update", and "setdefault"                  |
|                                |                        | "__delitem__"、         |                                                      |
|                                |                        | "__iter__"、"__len__"   |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MappingView"                  | "Sized"                |                         | "__init__"、"__len__" 和 "__repr__"                  |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "ItemsView"                    | "MappingView"、"Set"   |                         | "__contains__"、"__iter__"                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "KeysView"                     | "MappingView"、"Set"   |                         | "__contains__"、"__iter__"                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "ValuesView"                   | "MappingView"、        |                         | "__contains__"、"__iter__"                           |
|                                | "Collection"           |                         |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "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__"                   |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Buffer" [1]                   |                        | "__buffer__"            |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+

-[ 註腳 ]-

[1] 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)".


集合抽象基底類別的詳細描述
==========================

class collections.abc.Container

   有提供 "__contains__()" 方法之類別的 ABC。

class collections.abc.Hashable

   有提供 "__hash__()" 方法之類別的 ABC。

class collections.abc.Sized

   有提供 "__len__()" 方法之類別的 ABC。

class collections.abc.Callable

   有提供 "__call__()" 方法之類別的 ABC。

   See 註釋 callable 物件 for details on how to use "Callable" in type
   annotations.

class collections.abc.Iterable

   有提供 "__iter__()" 方法之類別的 ABC。

   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 for sized iterable container classes.

   在 3.6 版被加入.

class collections.abc.Iterator

   有提供 "__iter__()" 和 "__next__()" 方法之類別的 ABC。另請參閱
   *iterator* 的定義。

class collections.abc.Reversible

   亦有提供 "__reversed__()" 方法之可疊代類別的 ABC。

   在 3.6 版被加入.

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.

   在 3.5 版被加入.

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

   唯讀且可變*序列*的 ABC。

   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)

      回傳 *value* 的第一個索引。

      如果找不到該值，則引發 "ValueError"。

      建議要支援 *start* 和 *stop* 引數，但並非必要。

      在 3.5 版的變更: The "index()" method gained support for the
      *stop* and *start* arguments.

   Deprecated since version 3.12, will be removed in version 3.17:
   "ByteString" ABC 已被棄用。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" 最初
   被設計為一個抽象類別，以作為 "bytes" 和 "bytearray" 的超型別
   (supertype)。然而由於 ABC 從未擁有任何方法，知道一個物件是
   "ByteString" 的實例從未真正告訴你任何關於該物件的有用資訊。其他常見
   的緩衝區型別如 "memoryview" 也從未被理解為 "ByteString" 的子型別（
   無論是在 runtime 還是由靜態型別檢查器）。更多詳細資訊請參閱 **PEP
   688**。

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

   唯讀且可變集合的 ABC。

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

   唯讀且可變*對映*的 ABC。

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

   ABCs for mapping, items, keys, and values *views*.

class collections.abc.Awaitable

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

   *Coroutine* objects and instances of the "Coroutine" ABC are all
   instances of this ABC.

   備註:

     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.

   在 3.5 版被加入.

class collections.abc.Coroutine

   ABC for *coroutine* compatible classes.  These implement the
   following methods, defined in 協程物件: "send()", "throw()", and
   "close()".  Custom implementations must also implement
   "__await__()".  All "Coroutine" instances are also instances of
   "Awaitable".

   備註:

     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".

   在 3.5 版被加入.

class collections.abc.AsyncIterable

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

   在 3.5 版被加入.

class collections.abc.AsyncIterator

   ABC for classes that provide "__aiter__" and "__anext__" methods.
   See also the definition of *asynchronous iterator*.

   在 3.5 版被加入.

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.

   在 3.6 版被加入.

class collections.abc.Buffer

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

   在 3.12 版被加入.


Examples and Recipes
====================

ABCs allow us to ask classes or instances if they provide particular
functionality, for example:

   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

Notes on using "Set" and "MutableSet" as a 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".

也參考:

  * OrderedSet recipe for an example built on "MutableSet".

  * 關於 ABC 的更多資訊請見 "abc" module 和 **PEP 3119**。
