Stop inheriting Sized in collection ABCs (#2658)

Instead define abstract __len__ in affected classes.

Fixes #2655 without breaking
rominf/ordered-set-stubs#1

stdlib/2/typing.pyi

@@ -144,7 +144,7 @@ class Container(Protocol[_T_co]):
     @abstractmethod
     def __contains__(self, x: object) -> bool: ...
 
-class Sequence(Iterable[_T_co], Container[_T_co], Sized, Reversible[_T_co], Generic[_T_co]):
+class Sequence(Iterable[_T_co], Container[_T_co], Reversible[_T_co], Generic[_T_co]):
     @overload
     @abstractmethod
     def __getitem__(self, i: int) -> _T_co: ...
@@ -157,6 +157,9 @@ class Sequence(Iterable[_T_co], Container[_T_co], Sized, Reversible[_T_co], Gene
     def __contains__(self, x: object) -> bool: ...
     def __iter__(self) -> Iterator[_T_co]: ...
     def __reversed__(self) -> Iterator[_T_co]: ...
+    # Implement Sized (but don't have it as a base class).
+    @abstractmethod
+    def __len__(self) -> int: ...
 
 class MutableSequence(Sequence[_T], Generic[_T]):
     @abstractmethod
@@ -187,7 +190,7 @@ class MutableSequence(Sequence[_T], Generic[_T]):
     def remove(self, object: _T) -> None: ...
     def __iadd__(self, x: Iterable[_T]) -> MutableSequence[_T]: ...
 
-class AbstractSet(Sized, Iterable[_T_co], Container[_T_co], Generic[_T_co]):
+class AbstractSet(Iterable[_T_co], Container[_T_co], Generic[_T_co]):
     @abstractmethod
     def __contains__(self, x: object) -> bool: ...
     # Mixin methods
@@ -201,6 +204,10 @@ class AbstractSet(Sized, Iterable[_T_co], Container[_T_co], Generic[_T_co]):
     def __xor__(self, s: AbstractSet[_T]) -> AbstractSet[Union[_T_co, _T]]: ...
     # TODO: argument can be any container?
     def isdisjoint(self, s: AbstractSet[Any]) -> bool: ...
+    # Implement Sized (but don't have it as a base class).
+    @abstractmethod
+    def __len__(self) -> int: ...
+
 
 class MutableSet(AbstractSet[_T], Generic[_T]):
     @abstractmethod
@@ -216,14 +223,14 @@ class MutableSet(AbstractSet[_T], Generic[_T]):
     def __ixor__(self, s: AbstractSet[_S]) -> MutableSet[Union[_T, _S]]: ...
     def __isub__(self, s: AbstractSet[Any]) -> MutableSet[_T]: ...
 
-class MappingView(Sized):
+class MappingView(object):
     def __len__(self) -> int: ...
 
-class ItemsView(AbstractSet[Tuple[_KT_co, _VT_co]], MappingView, Generic[_KT_co, _VT_co]):
+class ItemsView(MappingView, AbstractSet[Tuple[_KT_co, _VT_co]], Generic[_KT_co, _VT_co]):
     def __contains__(self, o: object) -> bool: ...
     def __iter__(self) -> Iterator[Tuple[_KT_co, _VT_co]]: ...
 
-class KeysView(AbstractSet[_KT_co], MappingView, Generic[_KT_co]):
+class KeysView(MappingView, AbstractSet[_KT_co], Generic[_KT_co]):
     def __contains__(self, o: object) -> bool: ...
     def __iter__(self) -> Iterator[_KT_co]: ...
 
@@ -238,7 +245,7 @@ class ContextManager(Protocol[_T_co]):
                  exc_value: Optional[BaseException],
                  traceback: Optional[TracebackType]) -> Optional[bool]: ...
 
-class Mapping(Iterable[_KT], Container[_KT], Sized, Generic[_KT, _VT_co]):
+class Mapping(Iterable[_KT], Container[_KT], Generic[_KT, _VT_co]):
     # TODO: We wish the key type could also be covariant, but that doesn't work,
     # see discussion in https: //github.com/python/typing/pull/273.
     @abstractmethod
@@ -256,6 +263,9 @@ class Mapping(Iterable[_KT], Container[_KT], Sized, Generic[_KT, _VT_co]):
     def itervalues(self) -> Iterator[_VT_co]: ...
     def iteritems(self) -> Iterator[Tuple[_KT, _VT_co]]: ...
     def __contains__(self, o: object) -> bool: ...
+    # Implement Sized (but don't have it as a base class).
+    @abstractmethod
+    def __len__(self) -> int: ...
 
 class MutableMapping(Mapping[_KT, _VT], Generic[_KT, _VT]):
     @abstractmethod

stdlib/3/typing.pyi

@@ -235,11 +235,18 @@ class Container(Protocol[_T_co]):
 
 if sys.version_info >= (3, 6):
     @runtime
-    class Collection(Sized, Iterable[_T_co], Container[_T_co], Protocol[_T_co]): ...
+    class Collection(Iterable[_T_co], Container[_T_co], Protocol[_T_co]):
+        # Implement Sized (but don't have it as a base class).
+        @abstractmethod
+        def __len__(self) -> int: ...
+
     _Collection = Collection
 else:
     @runtime
-    class _Collection(Sized, Iterable[_T_co], Container[_T_co], Protocol[_T_co]): ...
+    class _Collection(Iterable[_T_co], Container[_T_co], Protocol[_T_co]):
+        # Implement Sized (but don't have it as a base class).
+        @abstractmethod
+        def __len__(self) -> int: ...
 
 class Sequence(_Collection[_T_co], Reversible[_T_co], Generic[_T_co]):
     @overload
@@ -317,14 +324,14 @@ class MutableSet(AbstractSet[_T], Generic[_T]):
     def __ixor__(self, s: AbstractSet[_S]) -> MutableSet[Union[_T, _S]]: ...
     def __isub__(self, s: AbstractSet[Any]) -> MutableSet[_T]: ...
 
-class MappingView(Sized):
+class MappingView:
     def __len__(self) -> int: ...
 
-class ItemsView(AbstractSet[Tuple[_KT_co, _VT_co]], MappingView, Generic[_KT_co, _VT_co]):
+class ItemsView(MappingView, AbstractSet[Tuple[_KT_co, _VT_co]], Generic[_KT_co, _VT_co]):
     def __contains__(self, o: object) -> bool: ...
     def __iter__(self) -> Iterator[Tuple[_KT_co, _VT_co]]: ...
 
-class KeysView(AbstractSet[_KT_co], MappingView, Generic[_KT_co]):
+class KeysView(MappingView, AbstractSet[_KT_co], Generic[_KT_co]):
     def __contains__(self, o: object) -> bool: ...
     def __iter__(self) -> Iterator[_KT_co]: ...