Improve module name handling for local custom code

src/transformers/dynamic_module_utils.py

@@ -19,6 +19,7 @@
 import importlib
 import importlib.metadata
 import importlib.util
+import keyword
 import os
 import re
 import shutil
@@ -48,11 +49,36 @@
 
 
 def _sanitize_module_name(name: str) -> str:
+    r"""
+    Tries to sanitize a module name so that it can be used as a Python module.
+
+    The following transformations are applied:
+
+    1. Replace `.` in module names with `_dot_`.
+    2. Replace `-` in module names with `_hyphen_`.
+    3. If the module name starts with a digit, prepend it with `_`.
+    4. Warn if the sanitized name is a Python reserved keyword or not a valid identifier.
+
+    If the input name is already a valid identifier, it is returned unchanged.
     """
-    Replace `.` in module names with `_dot_` so that it doesn't
-    look like an import path separator.
-    """
-    return name.replace(".", "_dot_")
+    # We not replacing `\W` characters with `_` to avoid collisions. Because `_` is a very common
+    # separator used in module names, replacing `\W` with `_` would create too many collisions.
+    # Once a module is imported, it is cached in `sys.modules` and the second import would return
+    # the first module, which might not be the expected behavior if name collisions happen.
+    new_name = name.replace(".", "_dot_").replace("-", "_hyphen_")
+    if new_name and new_name[0].isdigit():
+        new_name = f"_{new_name}"
+    if keyword.iskeyword(new_name):
+        logger.warning(
+            f"The module name {new_name} (originally {name}) is a reserved keyword in Python. "
+            "Please rename the original module to avoid import issues."
+        )
+    elif not new_name.isidentifier():
+        logger.warning(
+            f"The module name {new_name} (originally {name}) is not a valid Python identifier. "
+            "Please rename the original module to avoid import issues."
+        )
+    return new_name
 
 
 _HF_REMOTE_CODE_LOCK = threading.Lock()