Reduce duplication of code between typing and typing_extensions (#7075)

Author: AlexWaygood

stdlib/@python2/typing.pyi

@@ -20,6 +20,7 @@ class TypeVar:
 
 _promote = object()
 
+# N.B. Keep this definition in sync with typing_extensions._SpecialForm
 class _SpecialForm(object):
     def __getitem__(self, typeargs: Any) -> object: ...
 
@@ -44,7 +45,7 @@ _F = TypeVar("_F", bound=Callable[..., Any])
 def final(f: _F) -> _F: ...
 def overload(f: _F) -> _F: ...
 
-Literal: _SpecialForm = ...
+Literal: _SpecialForm
 # TypedDict is a (non-subscriptable) special form.
 TypedDict: object
 

stdlib/@python2/typing_extensions.pyi

@@ -27,8 +27,9 @@ from typing import (  # noqa Y022
 _T = TypeVar("_T")
 _F = TypeVar("_F", bound=Callable[..., Any])
 
+# unfortunately we have to duplicate this class definition from typing.pyi or we break pytype
 class _SpecialForm:
-    def __getitem__(self, typeargs: Any) -> Any: ...
+    def __getitem__(self, typeargs: Any) -> object: ...
 
 # This alias for above is kept here for backwards compatibility.
 runtime = runtime_checkable

stdlib/typing.pyi

@@ -29,6 +29,7 @@ class TypeVar:
 # Used for an undocumented mypy feature. Does not exist at runtime.
 _promote = object()
 
+# N.B. Keep this definition in sync with typing_extensions._SpecialForm
 class _SpecialForm:
     def __getitem__(self, typeargs: Any) -> object: ...
     if sys.version_info >= (3, 10):
@@ -138,13 +139,9 @@ if sys.version_info >= (3, 9):
 # Predefined type variables.
 AnyStr = TypeVar("AnyStr", str, bytes)  # noqa: Y001
 
-if sys.version_info >= (3, 8):
-    # This class did actually exist in 3.7, but had a different base.
-    # We'll just pretend it didn't exist though: the main external use case for _ProtocolMeta is
-    # to inherit from for your own custom protocol metaclasses. If you're using 3.7, at runtime
-    # you'd use typing_extensions.Protocol, which would be unrelated to typing._ProtocolMeta and
-    # so you'd run into metaclass conflicts at runtime if you used typing._ProtocolMeta.
-    class _ProtocolMeta(ABCMeta): ...
+# Technically in 3.7 this inherited from GenericMeta. But let's not reflect that, since
+# type checkers tend to assume that Protocols all have the ABCMeta metaclass.
+class _ProtocolMeta(ABCMeta): ...
 
 # Abstract base classes.
 

stdlib/typing_extensions.pyi

@@ -35,8 +35,12 @@ from typing import (  # noqa Y022
 _T = TypeVar("_T")
 _F = TypeVar("_F", bound=Callable[..., Any])
 
+# unfortunately we have to duplicate this class definition from typing.pyi or we break pytype
 class _SpecialForm:
-    def __getitem__(self, typeargs: Any) -> Any: ...
+    def __getitem__(self, typeargs: Any) -> object: ...
+    if sys.version_info >= (3, 10):
+        def __or__(self, other: Any) -> _SpecialForm: ...
+        def __ror__(self, other: Any) -> _SpecialForm: ...
 
 # This alias for above is kept here for backwards compatibility.
 runtime = runtime_checkable
@@ -51,11 +55,6 @@ Literal: _SpecialForm
 
 def IntVar(name: str) -> Any: ...  # returns a new TypeVar
 
-if sys.version_info < (3, 8):
-    # Technically in 3.6 this inherited from GenericMeta. But let's not reflect that, since
-    # type checkers tend to assume that Protocols all have the ABCMeta metaclass.
-    class _ProtocolMeta(abc.ABCMeta): ...
-
 # Internal mypy fallback type for all typed dicts (does not exist at runtime)
 class _TypedDict(Mapping[str, object], metaclass=abc.ABCMeta):
     __required_keys__: frozenset[str]