TYP: Fix typing in ExtensionDtype registry

pandas/core/dtypes/base.py

@@ -28,7 +28,7 @@
     from pandas.core.arrays import ExtensionArray
 
     # To parameterize on same ExtensionDtype
-    E = TypeVar("E", bound="ExtensionDtype")
+    ExtensionDtypeT = TypeVar("ExtensionDtypeT", bound="ExtensionDtype")
 
 
 class ExtensionDtype:
@@ -213,7 +213,7 @@ def construct_array_type(cls) -> type_t[ExtensionArray]:
         raise NotImplementedError
 
     @classmethod
-    def construct_from_string(cls, string: str):
+    def construct_from_string(cls, string: str) -> ExtensionDtype:
         r"""
         Construct this type from a string.
 
@@ -368,7 +368,7 @@ def _get_common_dtype(self, dtypes: list[DtypeObj]) -> DtypeObj | None:
             return None
 
 
-def register_extension_dtype(cls: type[E]) -> type[E]:
+def register_extension_dtype(cls: type[ExtensionDtypeT]) -> type[ExtensionDtypeT]:
     """
     Register an ExtensionType with pandas as class decorator.
 
@@ -424,20 +424,23 @@ def register(self, dtype: type[ExtensionDtype]) -> None:
 
         self.dtypes.append(dtype)
 
-    def find(self, dtype: type[ExtensionDtype] | str) -> type[ExtensionDtype] | None:
+    def find(
+        self, dtype: type[ExtensionDtype] | ExtensionDtype | str
+    ) -> type[ExtensionDtype] | ExtensionDtype | None:
         """
         Parameters
         ----------
-        dtype : Type[ExtensionDtype] or str
+        dtype : Type[ExtensionDtype] or ExtensionDtype or str
 
         Returns
         -------
         return the first matching dtype, otherwise return None
         """
         if not isinstance(dtype, str):
-            dtype_type = dtype
             if not isinstance(dtype, type):
                 dtype_type = type(dtype)
+            else:
+                dtype_type = dtype
             if issubclass(dtype_type, ExtensionDtype):
                 return dtype