| :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 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 |
| 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`. |