Fix dynamic module import error (#21646)

* fix dynamic module import error

---------
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

src/transformers/dynamic_module_utils.py

@@ -18,7 +18,9 @@ import importlib
 import os
 import re
 import shutil
+import subprocess
 import sys
+import tempfile
 from pathlib import Path
 from typing import Dict, Optional, Union
 
@@ -143,9 +145,25 @@ def get_class_in_module(class_name, module_path):
     """
     Import a module on the cache directory for modules and extract a class from it.
     """
-    module_path = module_path.replace(os.path.sep, ".")
-    module = importlib.import_module(module_path)
-    return getattr(module, class_name)
+    with tempfile.TemporaryDirectory() as tmp_dir:
+        module_dir = Path(HF_MODULES_CACHE) / os.path.dirname(module_path)
+        module_file_name = module_path.split(os.path.sep)[-1] + ".py"
+
+        # Copy to a temporary directory. We need to do this in another process to avoid strange and flaky error
+        # `ModuleNotFoundError: No module named 'transformers_modules.[module_dir_name].modeling'`
+        shutil.copy(f"{module_dir}/{module_file_name}", tmp_dir)
+        # On Windows, we need this character `r` before the path argument of `os.remove`
+        cmd = f'import os; os.remove(r"{module_dir}{os.path.sep}{module_file_name}")'
+        subprocess.run(["python", "-c", cmd])
+
+        # copy back the file that we want to import
+        shutil.copyfile(f"{tmp_dir}/{module_file_name}", f"{module_dir}/{module_file_name}")
+
+        # import the module
+        module_path = module_path.replace(os.path.sep, ".")
+        module = importlib.import_module(module_path)
+
+        return getattr(module, class_name)
 
 
 def get_cached_module_file(
@@ -212,7 +230,7 @@ def get_cached_module_file(
     # Download and cache module_file from the repo `pretrained_model_name_or_path` of grab it if it's a local file.
     pretrained_model_name_or_path = str(pretrained_model_name_or_path)
     if os.path.isdir(pretrained_model_name_or_path):
-        submodule = "local"
+        submodule = pretrained_model_name_or_path.split(os.path.sep)[-1]
     else:
         submodule = pretrained_model_name_or_path.replace("/", os.path.sep)
 
@@ -240,7 +258,7 @@ def get_cached_module_file(
     full_submodule = TRANSFORMERS_DYNAMIC_MODULE_NAME + os.path.sep + submodule
     create_dynamic_module(full_submodule)
     submodule_path = Path(HF_MODULES_CACHE) / full_submodule
-    if submodule == "local":
+    if submodule == pretrained_model_name_or_path.split(os.path.sep)[-1]:
         # We always copy local files (we could hash the file to see if there was a change, and give them the name of
         # that hash, to only copy when there is a modification but it seems overkill for now).
         # The only reason we do the copy is to avoid putting too many folders in sys.path.