# Copyright 2007 Google, Inc. All Rights Reserved.
# Licensed to PSF under a Contributor Agreement.
"""Abstract Base Classes (ABCs) according to PEP 3119."""
def abstractmethod(funcobj):
"""A decorator indicating abstract methods.
Requires that the metaclass is ABCMeta or derived from it. A
class that has a metaclass derived from ABCMeta cannot be
instantiated unless all of its abstract methods are overridden.
The abstract methods can be called using any of the normal
'super' call mechanisms. abstractmethod() may be used to declare
abstract methods for properties and descriptors.
Usage:
class C(metaclass=ABCMeta):
@abstractmethod
def my_abstract_method(self, arg1, arg2, argN):
...
"""
funcobj.__isabstractmethod__ = True
return funcobj
class abstractclassmethod(classmethod):
"""A decorator indicating abstract classmethods.
Deprecated, use 'classmethod' with 'abstractmethod' instead:
class C(ABC):
@classmethod
@abstractmethod
def my_abstract_classmethod(cls, ...):
...
"""
__isabstractmethod__ = True
def __init__(self, callable):
callable.__isabstractmethod__ = True
super().__init__(callable)
class abstractstaticmethod(staticmethod):
"""A decorator indicating abstract staticmethods.
Deprecated, use 'staticmethod' with 'abstractmethod' instead:
class C(ABC):
@staticmethod
@abstractmethod
def my_abstract_staticmethod(...):
...
"""
__isabstractmethod__ = True
def __init__(self, callable):
callable.__isabstractmethod__ = True
super().__init__(callable)
class abstractproperty(property):
"""A decorator indicating abstract properties.
Deprecated, use 'property' with 'abstractmethod' instead:
class C(ABC):
@property
@abstractmethod
def my_abstract_property(self):
...
"""
__isabstractmethod__ = True
try:
from _abc import (get_cache_token, _abc_init, _abc_register,
_abc_instancecheck, _abc_subclasscheck, _get_dump,
_reset_registry, _reset_caches)
except ImportError:
from _py_abc import ABCMeta, get_cache_token
ABCMeta.__module__ = 'abc'
else:
class ABCMeta(type):
"""Metaclass for defining Abstract Base Classes (ABCs).
Use this metaclass to create an ABC. An ABC can be subclassed
directly, and then acts as a mix-in class. You can also register
unrelated concrete classes (even built-in classes) and unrelated
ABCs as 'virtual subclasses' -- these and their descendants will
be considered subclasses of the registering ABC by the built-in
issubclass() function, but the registering ABC won't show up in
their MRO (Method Resolution Order) nor will method
implementations defined by the registering ABC be callable (not
even via super()).
"""
def __new__(mcls, name, bases, namespace, /, **kwargs):
cls = super().__new__(mcls, name, bases, namespace, **kwargs)
_abc_init(cls)
return cls
def register(cls, subclass):
"""Register a virtual subclass of an ABC.
Returns the subclass, to allow usage as a class decorator.
"""
return _abc_register(cls, subclass)
def __instancecheck__(cls, instance):
"""Override for isinstance(instance, cls)."""
return _abc_instancecheck(cls, instance)
def __subclasscheck__(cls, subclass):
"""Override for issubclass(subclass, cls)."""
return _abc_subclasscheck(cls, subclass)
def _dump_registry(cls, file=None):
"""Debug helper to print the ABC registry."""
print(f"Class: {cls.__module__}.{cls.__qualname__}", file=file)
print(f"Inv. counter: {get_cache_token()}", file=file)
(_abc_registry, _abc_cache, _abc_negative_cache,
_abc_negative_cache_version) = _get_dump(cls)
print(f"_abc_registry: {_abc_registry!r}", file=file)
print(f"_abc_cache: {_abc_cache!r}", file=file)
print(f"_abc_negative_cache: {_abc_negative_cache!r}", file=file)
print(f"_abc_negative_cache_version: {_abc_negative_cache_version!r}",
file=file)
def _abc_registry_clear(cls):
"""Clear the registry (for debugging or testing)."""
_reset_registry(cls)
def _abc_caches_clear(cls):
"""Clear the caches (for debugging or testing)."""
_reset_caches(cls)
def update_abstractmethods(cls):
"""Recalculate the set of abstract methods of an abstract class.
If a class has had one of its abstract methods implemented after the
class was created, the method will not be considered implemented until
this function is called. Alternatively, if a new abstract method has been
added to the class, it will only be considered an abstract method of the
class after this function is called.
This function should be called before any use is made of the class,
usually in class decorators that add methods to the subject class.
Returns cls, to allow usage as a class decorator.
If cls is not an instance of ABCMeta, does nothing.
"""
if not hasattr(cls, '__abstractmethods__'):
# We check for __abstractmethods__ here because cls might by a C
# implementation or a python implementation (especially during
# testing), and we want to handle both cases.
return cls
abstracts = set()
# Check the existing abstract methods of the parents, keep only the ones
# that are not implemented.
for scls in cls.__bases__:
for name in getattr(scls, '__abstractmethods__', ()):
value = getattr(cls, name, None)
if getattr(value, "__isabstractmethod__", False):
abstracts.add(name)
# Also add any other newly added abstract methods.
for name, value in cls.__dict__.items():
if getattr(value, "__isabstractmethod__", False):
abstracts.add(name)
cls.__abstractmethods__ = frozenset(abstracts)
return cls
[docs]
class ABC(metaclass=ABCMeta):
"""Helper class that provides a standard way to create an ABC using
inheritance.
"""
__slots__ = ()