Fix faulty rstrip in module loading (#31108)

src/transformers/dynamic_module_utils.py

@@ -198,7 +198,10 @@ def get_class_in_module(class_name: str, module_path: Union[str, os.PathLike]) -
     Returns:
         `typing.Type`: The class looked for.
     """
-    name = os.path.normpath(module_path).rstrip(".py").replace(os.path.sep, ".")
+    name = os.path.normpath(module_path)
+    if name.endswith(".py"):
+        name = name[:-3]
+    name = name.replace(os.path.sep, ".")
     module_spec = importlib.util.spec_from_file_location(name, location=Path(HF_MODULES_CACHE) / module_path)
     module = sys.modules.get(name)
     if module is None: