New in version 3.3: Formerly, this module was part of the collections
module.
Source code: Lib/_collections_abc.py
This module provides abstract base classes 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.
The collections module offers the following ABCs:
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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
ABC for sized iterable container classes.
New in version 3.6.
class collections.abc.Iterator
ABC for classes that provide the __iter__()
and __next__()
methods. See also the definition of iterator.
class collections.abc.Reversible
ABC for iterable classes that also provide the __reversed__()
method.
New 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. See also the definition of generator.
New in version 3.5.
class collections.abc.Sequence
class collections.abc.MutableSequence
class collections.abc.ByteString
ABCs for read-only and mutable sequences.
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.
Changed in version 3.5: The index() method added support for stop and start arguments.
class collections.abc.Set
class collections.abc.MutableSet
ABCs for read-only and mutable sets.
class collections.abc.Mapping
class collections.abc.MutableMapping
ABCs for read-only and mutable mappings.
class collections.abc.MappingView
class collections.abc.ItemsView
class collections.abc.KeysView
class collections.abc.ValuesView
ABCs for mapping, items, keys, and values views.
class collections.abc.Awaitable
ABC for awaitable objects, which can be used in await
expressions. Custom implementations must provide the __await__()
method.
Coroutine objects and instances of the Coroutine
ABC are all instances of this ABC.
Note
In CPython, generator-based coroutines (generators decorated with types.coroutine()
or asyncio.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.
New in version 3.5.
class collections.abc.Coroutine
ABC for coroutine compatible classes. These implement the following methods, defined in Coroutine Objects: send()
, throw()
, and close()
. Custom implementations must also implement __await__()
. All Coroutine
instances are also instances of Awaitable
. See also the definition of coroutine.
Note
In CPython, generator-based coroutines (generators decorated with types.coroutine()
or asyncio.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.
New in version 3.5.
class collections.abc.AsyncIterable
ABC for classes that provide __aiter__
method. See also the definition of asynchronous iterable.
New in version 3.5.
class collections.abc.AsyncIterator
ABC for classes that provide __aiter__
and __anext__
methods. See also the definition of asynchronous iterator.
New in version 3.5.
class collections.abc.AsyncGenerator
ABC for asynchronous generator classes that implement the protocol defined in PEP 525 and PEP 492.
New in version 3.6.
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 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
Notes on using Set
and MutableSet
as a mixin:
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 that can construct new instances from an iterable argument.__le__()
and __ge__()
, then the other operations will automatically follow suit.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
.See also
MutableSet
.abc
module and PEP 3119.
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Licensed under the PSF License.
https://docs.python.org/3.9/library/collections.abc.html