Simplify cattrs._compat.is_typeddict (#384)

* Simplify `cattrs._compat.is_typeddict`

* Add `ExceptionGroup` to `__all__` as well

* Fix the failing generic-typeddict test

* More unnecessary imports of `_TypedDictMeta`

* Changelog

* Brackets

Author: AlexWaygood

HISTORY.md

@@ -9,6 +9,7 @@
 - Optimize and improve unstructuring of `Optional` (unions of one type and `None`).
   ([#380](https://github.com/python-attrs/cattrs/issues/380) [#381](https://github.com/python-attrs/cattrs/pull/381))
 - Fix `format_exception` and `transform_error` type annotations.
+- Improve the implementation of `cattrs._compat.is_typeddict`. The implementation is now simpler, and relies on fewer private implementation details from `typing` and typing_extensions. ([#384](https://github.com/python-attrs/cattrs/pull/384))
 
 ## 23.1.2 (2023-06-02)
 

src/cattrs/_compat.py

@@ -20,16 +20,13 @@
 from attr import fields as attrs_fields
 from attr import resolve_types
 
+__all__ = ["ExceptionGroup", "ExtensionsTypedDict", "TypedDict", "is_typeddict"]
+
 try:
     from typing_extensions import TypedDict as ExtensionsTypedDict
 except ImportError:
     ExtensionsTypedDict = None
 
-try:
-    from typing_extensions import _TypedDictMeta as ExtensionsTypedDictMeta
-except ImportError:
-    ExtensionsTypedDictMeta = None
-
 if sys.version_info >= (3, 8):
     from typing import Final, Protocol, get_args, get_origin
 
@@ -44,9 +41,20 @@ def get_origin(cl):
     from typing_extensions import Final, Protocol
 
 if sys.version_info >= (3, 11):
-    ExceptionGroup = ExceptionGroup
+    from builtins import ExceptionGroup
 else:
-    from exceptiongroup import ExceptionGroup as ExceptionGroup  # noqa: PLC0414
+    from exceptiongroup import ExceptionGroup
+
+try:
+    from typing_extensions import is_typeddict as _is_typeddict
+except ImportError:
+    assert sys.version_info >= (3, 10)
+    from typing import is_typeddict as _is_typeddict
+
+
+def is_typeddict(cls):
+    """Thin wrapper around typing(_extensions).is_typeddict"""
+    return _is_typeddict(getattr(cls, "__origin__", cls))
 
 
 def has(cls):
@@ -157,7 +165,6 @@ def get_final_base(type) -> Optional[type]:
         _AnnotatedAlias,
         _GenericAlias,
         _SpecialGenericAlias,
-        _TypedDictMeta,
         _UnionGenericAlias,
     )
 
@@ -234,20 +241,6 @@ def get_newtype_base(typ: Any) -> Optional[type]:
                 return supertype
             return None
 
-    def is_typeddict(cls) -> bool:
-        return (
-            cls.__class__ is _TypedDictMeta
-            or (is_generic(cls) and (cls.__origin__.__class__ is _TypedDictMeta))
-            or (
-                ExtensionsTypedDictMeta is not None
-                and cls.__class__ is ExtensionsTypedDictMeta
-                or (
-                    is_generic(cls)
-                    and (cls.__origin__.__class__ is ExtensionsTypedDictMeta)
-                )
-            )
-        )
-
     def get_notrequired_base(type) -> "Union[Any, Literal[NOTHING]]":
         if get_origin(type) in (NotRequired, Required):
             return get_args(type)[0]
@@ -364,9 +357,8 @@ def copy_with(type, args):
     from typing_extensions import get_origin as te_get_origin
 
     if sys.version_info >= (3, 8):
-        from typing import TypedDict, _TypedDictMeta
+        from typing import TypedDict
     else:
-        _TypedDictMeta = None
         TypedDict = ExtensionsTypedDict
 
     def is_annotated(type) -> bool:
@@ -462,20 +454,6 @@ def copy_with(type, args):
         """Replace a generic type's arguments."""
         return type.copy_with(args)
 
-    def is_typeddict(cls) -> bool:
-        return (
-            cls.__class__ is _TypedDictMeta
-            or (is_generic(cls) and (cls.__origin__.__class__ is _TypedDictMeta))
-            or (
-                ExtensionsTypedDictMeta is not None
-                and cls.__class__ is ExtensionsTypedDictMeta
-                or (
-                    is_generic(cls)
-                    and (cls.__origin__.__class__ is ExtensionsTypedDictMeta)
-                )
-            )
-        )
-
     def get_notrequired_base(type) -> "Union[Any, Literal[NOTHING]]":
         if get_origin(type) in (NotRequired, Required):
             return get_args(type)[0]