192 lines
8.3 KiB
ReStructuredText
192 lines
8.3 KiB
ReStructuredText
: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>
|
|
|
|
.. versionadded:: 3.3
|
|
Formerly, this module was part of the :mod:`collections` module.
|
|
|
|
.. 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.
|
|
|
|
|
|
.. _collections-abstract-base-classes:
|
|
|
|
Collections Abstract Base Classes
|
|
---------------------------------
|
|
|
|
The collections module offers the following :term:`ABCs <abstract base class>`:
|
|
|
|
.. tabularcolumns:: |l|L|L|L|
|
|
|
|
========================= ===================== ====================== ====================================================
|
|
ABC Inherits from 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`, ``__len__`` ``index``, and ``count``
|
|
:class:`Container`
|
|
|
|
:class:`MutableSequence` :class:`Sequence` ``__getitem__``, Inherited :class:`Sequence` methods and
|
|
``__setitem__``, ``append``, ``reverse``, ``extend``, ``pop``,
|
|
``__delitem__``, ``remove``, and ``__iadd__``
|
|
``__len__``,
|
|
``insert``
|
|
|
|
:class:`Set` :class:`Sized`, ``__contains__``, ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``,
|
|
:class:`Iterable`, ``__iter__``, ``__gt__``, ``__ge__``, ``__and__``, ``__or__``,
|
|
:class:`Container` ``__len__`` ``__sub__``, ``__xor__``, and ``isdisjoint``
|
|
|
|
:class:`MutableSet` :class:`Set` ``__contains__``, Inherited :class:`Set` methods and
|
|
``__iter__``, ``clear``, ``pop``, ``remove``, ``__ior__``,
|
|
``__len__``, ``__iand__``, ``__ixor__``, and ``__isub__``
|
|
``add``,
|
|
``discard``
|
|
|
|
:class:`Mapping` :class:`Sized`, ``__getitem__``, ``__contains__``, ``keys``, ``items``, ``values``,
|
|
:class:`Iterable`, ``__iter__``, ``get``, ``__eq__``, and ``__ne__``
|
|
:class:`Container` ``__len__``
|
|
|
|
:class:`MutableMapping` :class:`Mapping` ``__getitem__``, Inherited :class:`Mapping` methods and
|
|
``__setitem__``, ``pop``, ``popitem``, ``clear``, ``update``,
|
|
``__delitem__``, and ``setdefault``
|
|
``__iter__``,
|
|
``__len__``
|
|
|
|
|
|
:class:`MappingView` :class:`Sized` ``__len__``
|
|
:class:`ItemsView` :class:`MappingView`, ``__contains__``,
|
|
:class:`Set` ``__iter__``
|
|
:class:`KeysView` :class:`MappingView`, ``__contains__``,
|
|
:class:`Set` ``__iter__``
|
|
:class:`ValuesView` :class:`MappingView` ``__contains__``, ``__iter__``
|
|
========================= ===================== ====================== ====================================================
|
|
|
|
|
|
.. class:: Container
|
|
Hashable
|
|
Sized
|
|
Callable
|
|
|
|
ABCs for classes that provide respectively the methods :meth:`__contains__`,
|
|
:meth:`__hash__`, :meth:`__len__`, and :meth:`__call__`.
|
|
|
|
.. class:: Iterable
|
|
|
|
ABC for classes that provide the :meth:`__iter__` method.
|
|
See also the definition of :term:`iterable`.
|
|
|
|
.. class:: Iterator
|
|
|
|
ABC for classes that provide the :meth:`~iterator.__iter__` and
|
|
:meth:`~iterator.__next__` methods. See also the definition of
|
|
:term:`iterator`.
|
|
|
|
.. class:: Sequence
|
|
MutableSequence
|
|
|
|
ABCs for read-only and mutable :term:`sequences <sequence>`.
|
|
|
|
.. class:: Set
|
|
MutableSet
|
|
|
|
ABCs for read-only and mutable sets.
|
|
|
|
.. class:: Mapping
|
|
MutableMapping
|
|
|
|
ABCs for read-only and mutable :term:`mappings <mapping>`.
|
|
|
|
.. class:: MappingView
|
|
ItemsView
|
|
KeysView
|
|
ValuesView
|
|
|
|
ABCs for mapping, items, keys, and values :term:`views <view>`.
|
|
|
|
|
|
These 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 :class:`Set` API, it is 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.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 :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 :meth:`__ge__`,
|
|
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/>`_ for an
|
|
example built on :class:`MutableSet`.
|
|
|
|
* For more about ABCs, see the :mod:`abc` module and :pep:`3119`.
|