Anti-registration of various ABC methods.
- Issue #25958: Support "anti-registration" of special methods from
various ABCs, like __hash__, __iter__ or __len__. All these (and
several more) can be set to None in an implementation class and the
behavior will be as if the method is not defined at all.
(Previously, this mechanism existed only for __hash__, to make
mutable classes unhashable.) Code contributed by Andrew Barnert and
Ivan Levkivskyi.
diff --git a/Lib/_collections_abc.py b/Lib/_collections_abc.py
index ffee385..077bde4 100644
--- a/Lib/_collections_abc.py
+++ b/Lib/_collections_abc.py
@@ -62,6 +62,18 @@
### ONE-TRICK PONIES ###
+def _check_methods(C, *methods):
+ mro = C.__mro__
+ for method in methods:
+ for B in mro:
+ if method in B.__dict__:
+ if B.__dict__[method] is None:
+ return NotImplemented
+ break
+ else:
+ return NotImplemented
+ return True
+
class Hashable(metaclass=ABCMeta):
__slots__ = ()
@@ -73,11 +85,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Hashable:
- for B in C.__mro__:
- if "__hash__" in B.__dict__:
- if B.__dict__["__hash__"]:
- return True
- break
+ return _check_methods(C, "__hash__")
return NotImplemented
@@ -92,11 +100,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Awaitable:
- for B in C.__mro__:
- if "__await__" in B.__dict__:
- if B.__dict__["__await__"]:
- return True
- break
+ return _check_methods(C, "__await__")
return NotImplemented
@@ -137,14 +141,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Coroutine:
- mro = C.__mro__
- for method in ('__await__', 'send', 'throw', 'close'):
- for base in mro:
- if method in base.__dict__:
- break
- else:
- return NotImplemented
- return True
+ return _check_methods(C, '__await__', 'send', 'throw', 'close')
return NotImplemented
@@ -162,8 +159,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is AsyncIterable:
- if any("__aiter__" in B.__dict__ for B in C.__mro__):
- return True
+ return _check_methods(C, "__aiter__")
return NotImplemented
@@ -182,9 +178,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is AsyncIterator:
- if (any("__anext__" in B.__dict__ for B in C.__mro__) and
- any("__aiter__" in B.__dict__ for B in C.__mro__)):
- return True
+ return _check_methods(C, "__anext__", "__aiter__")
return NotImplemented
@@ -200,8 +194,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Iterable:
- if any("__iter__" in B.__dict__ for B in C.__mro__):
- return True
+ return _check_methods(C, "__iter__")
return NotImplemented
@@ -220,9 +213,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Iterator:
- if (any("__next__" in B.__dict__ for B in C.__mro__) and
- any("__iter__" in B.__dict__ for B in C.__mro__)):
- return True
+ return _check_methods(C, '__iter__', '__next__')
return NotImplemented
Iterator.register(bytes_iterator)
@@ -246,16 +237,13 @@
@abstractmethod
def __reversed__(self):
- return NotImplemented
+ while False:
+ yield None
@classmethod
def __subclasshook__(cls, C):
if cls is Reversible:
- for B in C.__mro__:
- if "__reversed__" in B.__dict__:
- if B.__dict__["__reversed__"] is not None:
- return True
- break
+ return _check_methods(C, "__reversed__", "__iter__")
return NotImplemented
@@ -302,17 +290,10 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Generator:
- mro = C.__mro__
- for method in ('__iter__', '__next__', 'send', 'throw', 'close'):
- for base in mro:
- if method in base.__dict__:
- break
- else:
- return NotImplemented
- return True
+ return _check_methods(C, '__iter__', '__next__',
+ 'send', 'throw', 'close')
return NotImplemented
-
Generator.register(generator)
@@ -327,8 +308,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Sized:
- if any("__len__" in B.__dict__ for B in C.__mro__):
- return True
+ return _check_methods(C, "__len__")
return NotImplemented
@@ -343,8 +323,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Container:
- if any("__contains__" in B.__dict__ for B in C.__mro__):
- return True
+ return _check_methods(C, "__contains__")
return NotImplemented
@@ -359,8 +338,7 @@
@classmethod
def __subclasshook__(cls, C):
if cls is Callable:
- if any("__call__" in B.__dict__ for B in C.__mro__):
- return True
+ return _check_methods(C, "__call__")
return NotImplemented
@@ -640,6 +618,8 @@
return NotImplemented
return dict(self.items()) == dict(other.items())
+ __reversed__ = None
+
Mapping.register(mappingproxy)