fix: improve error handling for missing device attributes in DeviceCo…

bec_lib/bec_lib/devicemanager.py

@@ -95,12 +95,10 @@ def __contains__(self, key: object) -> bool:
         return super().__contains__(key)
 
     def __getattr__(self, attr):
-        if attr.startswith("_"):
-            # if dunder attributes are would not be caught, they
-            # would raise a DeviceConfigError and kill the
-            # IPython completer
-            # pylint: disable=no-member
-            return super().__getattr__(attr)
+        if attr.startswith("__"):
+            # Keep missing dunder lookups as AttributeError so
+            # introspection and IPython completion can probe safely.
+            raise AttributeError(f"{type(self).__name__!r} object has no attribute {attr!r}")
         dev = self.get(attr)
         if not dev:
             raise DeviceConfigError(f"Device {attr} does not exist.")

bec_lib/tests/test_devices.py

@@ -593,6 +593,11 @@ def test_device_container_wm_raises_for_missing_device(dev_container):
         dev_container.wm("missing")
 
 
+def test_device_container_getattr_raises_for_missing_single_underscore_device(dev_container):
+    with pytest.raises(DeviceConfigError, match="Device _something does not exist\\."):
+        dev_container._something
+
+
 def test_device_container_wm_raises_for_unmatched_glob(dev_container):
     with pytest.raises(DeviceConfigError, match="No devices match pattern miss\\*\\."):
         dev_container.wm("miss*")