fix multiphysics medium attribute lookup

tests/test_components/material/test_multi_physics.py

@@ -0,0 +1,39 @@
+import copy
+
+import pytest
+import tidy3d as td
+
+
+@pytest.fixture
+def dummy_optical():
+    return td.Medium(permittivity=1.0)
+
+
+def test_delegated_attributes_work(dummy_optical):
+    mp = td.MultiPhysicsMedium(optical=dummy_optical)
+
+    # delegated names resolve
+    assert mp.is_pec is dummy_optical.is_pec
+    assert mp._eps_plot == dummy_optical._eps_plot
+    assert mp.viz_spec == dummy_optical.viz_spec
+
+    # deepcopy still succeeds because __deepcopy__ is ignored
+    copy.deepcopy(mp)
+
+
+def test_delegated_attribute_without_optical_raises():
+    mp_no_opt = td.MultiPhysicsMedium(optical=None)
+
+    with pytest.raises(AttributeError, match=r"optical medium is 'None'"):
+        _ = mp_no_opt.is_pec
+
+
+def test_has_cached_props(dummy_optical):
+    mp = td.MultiPhysicsMedium(optical=dummy_optical)
+    mp._cached_properties
+
+
+def test_unknown_attribute_error(dummy_optical):
+    mp = td.MultiPhysicsMedium(optical=dummy_optical)
+    with pytest.raises(AttributeError, match=r"Did you mean to access the attribute of one"):
+        _ = mp.not_a_real_attribute

tidy3d/components/material/multi_physics.py

@@ -128,6 +128,12 @@ def __getattr__(self, name: str):
         Extend that mapping as additional cross-medium shim behaviour becomes
         necessary.
         """
+        # first check whether the attribute is already present
+        try:
+            return super().__getattr__(name)
+        except AttributeError:
+            pass
+
         IGNORED_ATTRIBUTES = ["__deepcopy__"]
         if name in IGNORED_ATTRIBUTES:
             return None
@@ -139,11 +145,18 @@ def __getattr__(self, name: str):
         }
 
         if name in DELEGATED_ATTRIBUTES:
-            return getattr(DELEGATED_ATTRIBUTES[name], name)
-        else:
-            raise ValueError(
-                f"MultiPhysicsMedium has no attribute called {name}. Did you mean to access the attribute of one of the optical, heat or charge media?"
-            )
+            sub = DELEGATED_ATTRIBUTES[name]
+            if sub is None:
+                raise AttributeError(
+                    f"Requested attribute {name!r}, but the optical medium is 'None' "
+                    " on this 'MultiPhysicsMedium' instance."
+                )
+            return getattr(sub, name)
+
+        raise AttributeError(
+            f"MultiPhysicsMedium has no attribute called {name}. "
+            "Did you mean to access the attribute of one of the optical, heat or charge media?"
+        )
 
     @property
     def heat_spec(self):