1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
|
: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.
**Source code:** :source:`Lib/_collections_abc.py`
.. testsetup:: *
from collections import *
import itertools
__name__ = '<doctest>'
--------------
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:`Generator` :class:`Iterator` ``send``, ``throw`` ``close``, ``__iter__``, ``__next__``
: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:`Awaitable` ``__await__``
:class:`Coroutine` :class:`Awaitable` ``send``, ``throw`` ``close``
:class:`AsyncIterable` ``__aiter__``
:class:`AsyncIterator` :class:`AsyncIterable` ``__anext__`` ``__aiter__``
========================== ====================== ======================= ====================================================
.. 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:: Generator
ABC for generator classes that implement the protocol defined in
:pep:`342` that extends iterators with the :meth:`~generator.send`,
:meth:`~generator.throw` and :meth:`~generator.close` methods.
See also the definition of :term:`generator`.
.. versionadded:: 3.5
.. class:: Sequence
MutableSequence
ABCs for read-only and mutable :term:`sequences <sequence>`.
Implementation note: Some of the mixin methods, such as
:meth:`__iter__`, :meth:`__reversed__` and :meth:`index`, make
repeated calls to the underlying :meth:`__getitem__` method.
Consequently, if :meth:`__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.
.. versionchanged:: 3.5
The index() method added support for *stop* and *start*
arguments.
.. 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 <dictionary view>`.
.. class:: Awaitable
ABC for :term:`awaitable` objects, which can be used in :keyword:`await`
expressions. Custom implementations must provide the :meth:`__await__`
method.
:term:`Coroutine` objects and instances of the
:class:`~collections.abc.Coroutine` ABC are all instances of this ABC.
.. note::
In CPython, generator-based coroutines (generators decorated with
:func:`types.coroutine` or :func:`asyncio.coroutine`) are
*awaitables*, even though they do not have an :meth:`__await__` method.
Using ``isinstance(gencoro, Awaitable)`` for them will return ``False``.
Use :func:`inspect.isawaitable` to detect them.
.. versionadded:: 3.5
.. class:: Coroutine
ABC for coroutine compatible classes. These implement the
following methods, defined in :ref:`coroutine-objects`:
:meth:`~coroutine.send`, :meth:`~coroutine.throw`, and
:meth:`~coroutine.close`. Custom implementations must also implement
:meth:`__await__`. All :class:`Coroutine` instances are also instances of
:class:`Awaitable`. See also the definition of :term:`coroutine`.
.. note::
In CPython, generator-based coroutines (generators decorated with
:func:`types.coroutine` or :func:`asyncio.coroutine`) are
*awaitables*, even though they do not have an :meth:`__await__` method.
Using ``isinstance(gencoro, Coroutine)`` for them will return ``False``.
Use :func:`inspect.isawaitable` to detect them.
.. versionadded:: 3.5
.. class:: AsyncIterable
ABC for classes that provide ``__aiter__`` method. See also the
definition of :term:`asynchronous iterable`.
.. versionadded:: 3.5
.. class:: AsyncIterator
ABC for classes that provide ``__aiter__`` and ``__anext__``
methods. See also the definition of :term:`asynchronous iterator`.
.. versionadded:: 3.5
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 hashability using mixins,
inherit from both :meth:`Set` and :meth:`Hashable`, then define
``__hash__ = Set._hash``.
.. seealso::
* `OrderedSet recipe <https://code.activestate.com/recipes/576694/>`_ for an
example built on :class:`MutableSet`.
* For more about ABCs, see the :mod:`abc` module and :pep:`3119`.
|
