collections.abc
--- Abstract Base Classes for Containers¶
Ajouté dans la version 3.3: Auparavant, ce module faisait partie du module collections
.
Code source : 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.
An issubclass()
or isinstance()
test for an interface works in one
of three ways.
1) A newly written class can inherit directly from one of the abstract base classes. The class must supply the required abstract methods. The remaining mixin methods come from inheritance and can be overridden if desired. Other methods may be added as needed:
class C(Sequence): # Direct inheritance
def __init__(self): ... # Extra method not required by the ABC
def __getitem__(self, index): ... # Required abstract method
def __len__(self): ... # Required abstract method
def count(self, value): ... # Optionally override a mixin method
>>> issubclass(C, Sequence)
True
>>> isinstance(C(), Sequence)
True
2) Existing classes and built-in classes can be registered as "virtual
subclasses" of the ABCs. Those classes should define the full API
including all of the abstract methods and all of the mixin methods.
This lets users rely on issubclass()
or isinstance()
tests
to determine whether the full interface is supported. The exception to
this rule is for methods that are automatically inferred from the rest
of the API:
class D: # No inheritance
def __init__(self): ... # Extra method not required by the ABC
def __getitem__(self, index): ... # Abstract method
def __len__(self): ... # Abstract method
def count(self, value): ... # Mixin method
def index(self, value): ... # Mixin method
Sequence.register(D) # Register instead of inherit
>>> issubclass(D, Sequence)
True
>>> isinstance(D(), Sequence)
True
In this example, class D
does not need to define
__contains__
, __iter__
, and __reversed__
because the
in-operator, the iteration
logic, and the reversed()
function automatically fall back to
using __getitem__
and __len__
.
3) Some simple interfaces are directly recognizable by the presence of
the required methods (unless those methods have been set to
None
):
class E:
def __iter__(self): ...
def __next__(self): ...
>>> issubclass(E, Iterable)
True
>>> isinstance(E(), Iterable)
True
Complex interfaces do not support this last technique because an
interface is more than just the presence of method names. Interfaces
specify semantics and relationships between methods that cannot be
inferred solely from the presence of specific method names. For
example, knowing that a class supplies __getitem__
, __len__
, and
__iter__
is insufficient for distinguishing a Sequence
from
a Mapping
.
Ajouté dans la version 3.9: These abstract classes now support []
. See Type Alias générique
and PEP 585.
Classes de base abstraites de collections¶
Le module collections apporte les ABC suivantes :
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Footnotes
Collections Abstract Base Classes -- Detailed Descriptions¶
- 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.Callable¶
ABC for classes that provide the
__call__()
method.See Annotating callable objects for details on how to use
Callable
in type annotations.
- class collections.abc.Iterable¶
ABC for classes that provide the
__iter__()
method.Checking
isinstance(obj, Iterable)
detects classes that are registered asIterable
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 calliter(obj)
.
- class collections.abc.Collection¶
ABC pour les classes de conteneurs itérables et sized.
Ajouté dans la version 3.6.
- class collections.abc.Iterator¶
ABC pour les classes qui définissent les méthodes
__iter__()
et__next__()
. Voir aussi la définition d'itérateur.
- class collections.abc.Reversible¶
ABC for iterable classes that also provide the
__reversed__()
method.Ajouté dans la 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()
andclose()
methods.See Annotating generators and coroutines for details on using
Generator
in type annotations.Ajouté dans la version 3.5.
- class collections.abc.Sequence¶
- class collections.abc.MutableSequence¶
ABC pour les séquences immuables et mutables.
Implementation note: Some of the mixin methods, such as
__iter__()
,__reversed__()
andindex()
, 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.Modifié dans la version 3.5: La méthode index() a ajouté le support des arguments start et stop.
- class collections.abc.Mapping¶
- class collections.abc.MutableMapping¶
ABC pour les tables de correspondances immuables et mutables.
- class collections.abc.MappingView¶
- class collections.abc.ItemsView¶
- class collections.abc.KeysView¶
- class collections.abc.ValuesView¶
ABC pour les vues de mappings (tableaux de correspondances), d'éléments, de clés et de valeurs.
- class collections.abc.Awaitable¶
ABC for awaitable objects, which can be used in
await
expressions. Custom implementations must provide the__await__()
method.Les objets coroutines et les instances de l'ABC
Coroutine
sont tous des instances de cette ABC.Note
In CPython, generator-based coroutines (generators decorated with
@types.coroutine
) are awaitables, even though they do not have an__await__()
method. Usingisinstance(gencoro, Awaitable)
for them will returnFalse
. Useinspect.isawaitable()
to detect them.Ajouté dans la version 3.5.
- class collections.abc.Coroutine¶
ABC for coroutine compatible classes. These implement the following methods, defined in Objets coroutines:
send()
,throw()
, andclose()
. Custom implementations must also implement__await__()
. AllCoroutine
instances are also instances ofAwaitable
.Note
In CPython, generator-based coroutines (generators decorated with
@types.coroutine
) are awaitables, even though they do not have an__await__()
method. Usingisinstance(gencoro, Coroutine)
for them will returnFalse
. Useinspect.isawaitable()
to detect them.See Annotating generators and coroutines for details on using
Coroutine
in type annotations. The variance and order of type parameters correspond to those ofGenerator
.Ajouté dans la version 3.5.
- class collections.abc.AsyncIterable¶
ABC for classes that provide an
__aiter__
method. See also the definition of asynchronous iterable.Ajouté dans la version 3.5.
- class collections.abc.AsyncIterator¶
ABC pour les classes qui définissent les méthodes
__aiter__
et__anext__
. Voir aussi la définition d'itérateur asynchrone.Ajouté dans la version 3.5.
- class collections.abc.AsyncGenerator¶
ABC for asynchronous generator classes that implement the protocol defined in PEP 525 and PEP 492.
See Annotating generators and coroutines for details on using
AsyncGenerator
in type annotations.Ajouté dans la version 3.6.
- class collections.abc.Buffer¶
ABC for classes that provide the
__buffer__()
method, implementing the buffer protocol. See PEP 688.Ajouté dans la version 3.12.
Examples and Recipes¶
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 à propos de l'utilisation de Set
et MutableSet
comme mixin :
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 internalclassmethod
called_from_iterable()
which callscls(iterable)
to produce a new set. If theSet
mixin is being used in a class with a different constructor signature, you will need to override_from_iterable()
with a classmethod or regular method that can construct new instances from an iterable argument.To override the comparisons (presumably for speed, as the semantics are fixed), redefine
__le__()
and__ge__()
, then the other operations will automatically follow suit.The
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 bothSet()
andHashable()
, then define__hash__ = Set._hash
.
Voir aussi
OrderedSet recipe pour un exemple construit sur
MutableSet
.Pour plus d'informations à propos des ABC, voir le module
abc
et la PEP 3119.