"collections.abc" --- コンテナの抽象基底クラス
**********************************************

Added in version 3.3: 以前はこのモジュールは "collections" モジュール
の一部でした。

**ソースコード:** Lib/_collections_abc.py

======================================================================

このモジュールは、 *抽象基底クラス* を提供します。抽象基底クラスは、ク
ラスが特定のインターフェースを提供しているか、例えば *ハッシュ可能* で
あるかや *マッピング* であるかを判定します。

"issubclass()" や "isinstance()" を使ったインターフェースに対するテス
トは、以下の3つのいずれかの方法で動作します。

1） 新しく定義したクラスは抽象基底クラスのいずれかを直接継承することが
できます。その場合クラスは必要な抽象メソッドを提供しなければなりません
。残りのミックスインメソッドは継承により引き継がれますが、必要ならオー
バーライドすることができます。その他のメソッドは必要に応じて追加するこ
とができます:

   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） 既存のクラスや組み込みのクラスを "仮想派生クラス" として ABC に登
録することができます。これらのクラスは、全ての抽象メソッドとミックスイ
ンメソッドを含む完全な API を定義する必要があります。これにより、その
クラスが完全なインターフェースをサポートしているかどうかを、ユーザーが
"issubclass()" や "isinstance()" で判断できるようになります。このルー
ルの例外は、残りの API から自動的に推測ができるようなメソッドです:

   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） いくつかの単純なインターフェースは、必要なメソッドの存在だけで (そ
れらのメソッドが "None" に設定されていなければ) 直接認識されます:

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

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

複雑なインターフェースは、単に特定のメソッドが存在すること以上の定義を
持つため、3番目のテクニックをサポートしていません。それらのインターフ
ェースはメソッドの意味やメソッド間の関係まで指定するので、特定のメソッ
ド名の存在からだけではインターフェースの推測ができません。たとえば、あ
るクラスが "__getitem__", "__len__", および "__iter__" を提供するとい
うだけでは、 "Sequence" と "Mapping" を区別するには不十分です。

Added in version 3.9: これらの抽象クラスは "[]" をサポートするようにな
りました。 ジェネリックエイリアス型 および **PEP 585** を参照してくだ
さい。


コレクション抽象基底クラス
==========================

collections モジュールは以下の *ABC (抽象基底クラス)* を提供します:

+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| ABC                            | 継承しているクラス     | 抽象メソッド            | mixin メソッド                                       |
|================================|========================|=========================|======================================================|
| "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__"               | "count"                                              |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableSequence"              | "Sequence"             | "__getitem__",          | Inherited "Sequence" methods and "append", "clear",  |
|                                |                        | "__setitem__",          | "reverse", "extend", "pop", "remove", and "__iadd__" |
|                                |                        | "__delitem__",          |                                                      |
|                                |                        | "__len__", "insert"     |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Set"                          | "Collection"           | "__contains__",         | "__le__", "__lt__", "__eq__", "__ne__", "__gt__",    |
|                                |                        | "__iter__", "__len__"   | "__ge__", "__and__", "__or__", "__sub__", "__xor__", |
|                                |                        |                         | "isdisjoint"                                         |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableSet"                   | "Set"                  | "__contains__",         | "Set" から継承したメソッドと、 "clear", "pop",       |
|                                |                        | "__iter__", "__len__",  | "remove", "__ior__", "__iand__", "__ixor__",         |
|                                |                        | "add", "discard"        | "__isub__"                                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Mapping"                      | "Collection"           | "__getitem__",          | "__contains__", "keys", "items", "values", "get",    |
|                                |                        | "__iter__", "__len__"   | "__eq__", "__ne__"                                   |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableMapping"               | "Mapping"              | "__getitem__",          | "Mapping" から継承したメソッドと、 "pop", "popitem", |
|                                |                        | "__setitem__",          | "clear", "update", "setdefault"                      |
|                                |                        | "__delitem__",          |                                                      |
|                                |                        | "__iter__", "__len__"   |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MappingView"                  | "Sized"                |                         | "__len__"                                            |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "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__"            |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+

-[ 脚注 ]-

[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)".


コレクションの抽象基底クラス -- 詳細な説明
==========================================

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

   サイズ付きのイテラブルなコンテナクラスの ABC です。

   Added in version 3.6.

class collections.abc.Iterator

   "__iter__()" メソッドと "__next__()" メソッドを提供するクラスの ABC
   です。 *iterator* の定義も参照してください。

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.

   Added in version 3.5.

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

   読み出し専用の *シーケンス* およびミュータブルな *シーケンス* の
   ABC です。

   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.

   バージョン 3.5 で変更: index() メソッドは *stop* と *start* 引数を
   サポートしました。

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

   ABCs for read-only and mutable sets.

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

   読み出し専用の *マッピング* およびミュータブルな *マッピング* の
   ABC です。

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

   マッピング、要素、キー、値の *ビュー* の ABC です。

class collections.abc.Awaitable

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

   "Coroutine" ABC の *Coroutine* オブジェクトとインスタンスは、すべて
   この ABC のインスタンスです。

   注釈:

     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 コルーチンオブジェクト: "send()",
   "throw()", and "close()".  Custom implementations must also
   implement "__await__()".  All "Coroutine" instances are also
   instances of "Awaitable".

   注釈:

     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.

   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

   "__aiter__" および "__anext__" メソッドを提供するクラスの ABC です
   。*asynchronous iterator* の定義も参照してください。

   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**.

   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.


例とレシピ
==========

抽象基底クラスは、クラスやインスタンスが特定の機能を提供しているかどう
かを調べることを可能にします。例えば:

   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

"Set" と "MutableSet" を mixin 型として利用するときの注意点:

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".

参考:

  * "MutableSet" を使った例として OrderedSet recipe。

  * ABCs についての詳細は、 "abc" モジュールと **PEP 3119** を参照して
    ください。
