Create custom class for no exist attribute in patch_attr (#2806)

Signed-off-by: Daemyung Jang <quic_daemyung@quicinc.com>

TrainingExtensions/torch/src/python/aimet_torch/experimental/v2/utils.py

@@ -118,7 +118,10 @@ def patch_attr(obj, attr_name, new_attr)-> _ContextManager:
         if attr_name in obj._parameters or attr_name in obj._buffers: # pylint: disable=protected-access
             return _patch_param_or_buffer(obj, attr_name, new_attr)
 
-    old_attr = getattr(obj, attr_name, None)
+    class _NullAttribute:
+        pass
+
+    old_attr = getattr(obj, attr_name, _NullAttribute())
     action = lambda: setattr(obj, attr_name, new_attr)
 
     def cleanup():
@@ -127,7 +130,7 @@ def cleanup():
         except AttributeError:
             pass
 
-        if not hasattr(obj, attr_name) and old_attr is not None:
+        if not hasattr(obj, attr_name) and not isinstance(old_attr, _NullAttribute):
             setattr(obj, attr_name, old_attr)
 
     return _ContextManager(action, cleanup)

TrainingExtensions/torch/test/python/experimental/v2/test_utils_.py

@@ -93,3 +93,8 @@ def test_patch_attr():
 
     replica = conv._replicate_for_data_parallel()
     assert replica.forward.__self__ is replica
+
+    with patch_attr(conv, 'no_exist_attribute', 1):
+        assert conv.no_exist_attribute == 1
+
+    assert not hasattr(conv, 'no_exist_attribute')