[Bugfix] Use sys.modules.get() to avoid KeyError in modeling_utils

src/transformers/modeling_utils.py

@@ -1948,9 +1948,9 @@ def _can_set_attn_implementation(cls) -> bool:
         """Detect whether the class supports setting its attention implementation dynamically. It is an ugly check based on
         opening the file, but avoids maintaining yet another property flag.
         """
-        class_module = sys.modules[cls.__module__]
+        class_module = sys.modules.get(cls.__module__)
         # This can happen for a custom model in a jupyter notebook or repl for example - simply do not allow to set it then
-        if not hasattr(class_module, "__file__"):
+        if class_module is None or not hasattr(class_module, "__file__"):
             return False
         class_file = class_module.__file__
         with open(class_file, "r", encoding="utf-8") as f:
@@ -1967,9 +1967,9 @@ def _can_set_experts_implementation(cls) -> bool:
         """Detect whether the class supports setting its experts implementation dynamically. It is an ugly check based on
         opening the file, but avoids maintaining yet another property flag.
         """
-        class_module = sys.modules[cls.__module__]
+        class_module = sys.modules.get(cls.__module__)
         # This can happen for a custom model in a jupyter notebook or repl for example - simply do not allow to set it then
-        if not hasattr(class_module, "__file__"):
+        if class_module is None or not hasattr(class_module, "__file__"):
             return False
         class_file = class_module.__file__
         with open(class_file, "r", encoding="utf-8") as f:

tests/utils/test_modeling_utils.py

@@ -2985,6 +2985,33 @@ def test_identical(self):
         self.assertEqual(identical_names, [])
 
 
+@require_torch
+class TestSysModulesMissing(unittest.TestCase):
+    """Regression test for #45003: KeyError when module absent from sys.modules."""
+
+    def test_can_set_attn_impl_missing_module(self):
+        from transformers.models.bert.modeling_bert import BertModel
+
+        key = BertModel.__module__
+        saved = sys.modules.pop(key, None)
+        try:
+            self.assertFalse(BertModel._can_set_attn_implementation())
+        finally:
+            if saved is not None:
+                sys.modules[key] = saved
+
+    def test_can_set_experts_impl_missing_module(self):
+        from transformers.models.bert.modeling_bert import BertModel
+
+        key = BertModel.__module__
+        saved = sys.modules.pop(key, None)
+        try:
+            self.assertFalse(BertModel._can_set_experts_implementation())
+        finally:
+            if saved is not None:
+                sys.modules[key] = saved
+
+
 @require_torch
 class TestSaveAndLoadModelWithExtraState(TestCasePlus):
     """