Fix StructureData inconsistent labels length error (#69)

* document RuntimeError

* use locals() instead of zip to avoid name-labels mismatch

* add test_structure_data_inconsistent_length()

* tweak test_structure_data_inconsistent_length assert

chgnet/data/dataset.py

@@ -45,18 +45,20 @@ def __init__(
             magmoms (list[list[float]], optional): [data_size, n_atoms, 1]
             graph_converter (CrystalGraphConverter, optional): Converts the structures to
                 graphs. If None, it will be set to CHGNet default converter.
+
+        Raises:
+            RuntimeError: if the length of structures and labels (energies, forces,
+                stresses, magmoms) are not equal.
         """
         for idx, struct in enumerate(structures):
             if not isinstance(struct, Structure):
                 raise ValueError(f"{idx} is not a pymatgen Structure object: {struct}")
-        for label, name in zip(
-            [energies, forces, stresses, magmoms],
-            ["energies, forces,stresses, magmoms"],
-        ):
-            if len(label) != len(structures):
-                raise ValueError(
-                    f"Error! inconsistent number of structures and labels: "
-                    f" len(structures)={len(structures)}, len({name})={len(label)})"
+        for name in "energies forces stresses magmoms".split():
+            labels = locals()[name]
+            if labels is not None and len(labels) != len(structures):
+                raise RuntimeError(
+                    f"Inconsistent number of structures and labels: "
+                    f"{len(structures)=}, len({name})={len(labels)}"
                 )
         self.structures = structures
         self.energies = energies

tests/test_dataset.py

@@ -60,3 +60,17 @@ def test_data_loader(structure_data: StructureData) -> None:
     assert targets["s"][0].shape == (3, 3)
     assert len(targets["m"]) == 16
     assert targets["m"][0].shape == (2, 1)
+
+
+def test_structure_data_inconsistent_length():
+    # https://github.com/CederGroupHub/chgnet/pull/69
+    structures = [NaCl.copy() for _ in range(5)]
+    energies = [np.random.random(1) for _ in range(5)]
+    forces = [np.random.random([2, 3]) for _ in range(4)]
+    with pytest.raises(RuntimeError) as exc:
+        StructureData(structures=structures, energies=energies, forces=forces)
+
+    assert (
+        str(exc.value)
+        == f"Inconsistent number of structures and labels: {len(structures)=}, {len(forces)=}"
+    )