Issue #11085: Moved collections abstract base classes into a separate module
called collections.abc, following the pattern used by importlib.abc. For
backwards compatibility, the names continue to also be imported into the
collections module.
diff --git a/Doc/library/collections.abc.rst b/Doc/library/collections.abc.rst
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+:mod:`collections.abc` --- Abstract Base Classes for Containers
+===============================================================
+
+.. module:: collections.abc
+ :synopsis: Abstract base classes for containers
+.. moduleauthor:: Raymond Hettinger <python at rcn.com>
+.. sectionauthor:: Raymond Hettinger <python at rcn.com>
+
+.. testsetup:: *
+
+ from collections import *
+ import itertools
+ __name__ = '<doctest>'
+
+**Source code:** :source:`Lib/collections/abc.py`
+
+--------------
+
+This module provides :term:`abstract base classes <abstract base class>` 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.
+
+.. versionchanged:: 3.3
+ Formerly, this module was part of the :mod:`collections` module.
+
+.. _abstract-base-classes:
+
+Collections Abstract Base Classes
+---------------------------------
+
+The collections module offers the following ABCs:
+
+========================= ===================== ====================== ====================================================
+ABC Inherits Abstract Methods Mixin Methods
+========================= ===================== ====================== ====================================================
+:class:`Container` ``__contains__``
+:class:`Hashable` ``__hash__``
+:class:`Iterable` ``__iter__``
+:class:`Iterator` :class:`Iterable` ``__next__`` ``__iter__``
+:class:`Sized` ``__len__``
+:class:`Callable` ``__call__``
+
+:class:`Sequence` :class:`Sized`, ``__getitem__`` ``__contains__``, ``__iter__``, ``__reversed__``,
+ :class:`Iterable`, ``index``, and ``count``
+ :class:`Container`
+
+:class:`MutableSequence` :class:`Sequence` ``__setitem__`` Inherited Sequence methods and
+ ``__delitem__``, ``append``, ``reverse``, ``extend``, ``pop``,
+ and ``insert`` ``remove``, and ``__iadd__``
+
+:class:`Set` :class:`Sized`, ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``,
+ :class:`Iterable`, ``__gt__``, ``__ge__``, ``__and__``, ``__or__``,
+ :class:`Container` ``__sub__``, ``__xor__``, and ``isdisjoint``
+
+:class:`MutableSet` :class:`Set` ``add`` and Inherited Set methods and
+ ``discard`` ``clear``, ``pop``, ``remove``, ``__ior__``,
+ ``__iand__``, ``__ixor__``, and ``__isub__``
+
+:class:`Mapping` :class:`Sized`, ``__getitem__`` ``__contains__``, ``keys``, ``items``, ``values``,
+ :class:`Iterable`, ``get``, ``__eq__``, and ``__ne__``
+ :class:`Container`
+
+:class:`MutableMapping` :class:`Mapping` ``__setitem__`` and Inherited Mapping methods and
+ ``__delitem__`` ``pop``, ``popitem``, ``clear``, ``update``,
+ and ``setdefault``
+
+
+:class:`MappingView` :class:`Sized` ``__len__``
+:class:`KeysView` :class:`MappingView`, ``__contains__``,
+ :class:`Set` ``__iter__``
+:class:`ItemsView` :class:`MappingView`, ``__contains__``,
+ :class:`Set` ``__iter__``
+:class:`ValuesView` :class:`MappingView` ``__contains__``, ``__iter__``
+========================= ===================== ====================== ====================================================
+
+These ABCs allow us to ask classes or instances if they provide
+particular functionality, for example::
+
+ size = None
+ if isinstance(myvar, collections.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 :class:`Set` API, it only necessary to supply the three underlying
+abstract methods: :meth:`__contains__`, :meth:`__iter__`, and :meth:`__len__`.
+The ABC supplies the remaining methods such as :meth:`__and__` and
+:meth:`isdisjoint` ::
+
+ class ListBasedSet(collections.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 :class:`Set` and :class:`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
+ :meth:`_from_iterable` which calls ``cls(iterable)`` to produce a new set.
+ If the :class:`Set` mixin is being used in a class with a different
+ constructor signature, you will need to override :meth:`from_iterable`
+ with a classmethod that can construct new instances from
+ an iterable argument.
+
+(2)
+ To override the comparisons (presumably for speed, as the
+ semantics are fixed), redefine :meth:`__le__` and
+ then the other operations will automatically follow suit.
+
+(3)
+ The :class:`Set` mixin provides a :meth:`_hash` method to compute a hash value
+ for the set; however, :meth:`__hash__` is not defined because not all sets
+ are hashable or immutable. To add set hashabilty using mixins,
+ inherit from both :meth:`Set` and :meth:`Hashable`, then define
+ ``__hash__ = Set._hash``.
+
+.. seealso::
+
+ * `OrderedSet recipe <http://code.activestate.com/recipes/576694/>`_ that uses
+ :class:`MutableSet`.
+
+ * For more about ABCs, see the :mod:`abc` module and :pep:`3119`.