Add record of single element attribute lists in IO

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### User-facing changes
 
+|fixed| Single element lists/sets in the model Dataset attribute dictionary are restored to lists/sets on loading from NetCDF (#614).
+
 |new| Decision variables and global expressions can have a `title` defined, which will be available in the model results as attributes of those components and can be used for e.g. visualisation (#582).
 Parameter titles from the model definition schema will also propagate to the model inputs.
 

src/calliope/io.py

@@ -15,6 +15,7 @@
 
 from calliope import exceptions
 from calliope.attrdict import AttrDict
+from calliope.util.tools import listify
 
 CONFIG_DIR = importlib.resources.files("calliope") / "config"
 
@@ -39,26 +40,33 @@ def read_netcdf(path):
 
 
 def _pop_serialised_list(
-    attrs: dict, serialised_items: Union[str, list, np.ndarray]
+    attrs: dict, serialised_items: Union[str, list]
 ) -> Union[list, np.ndarray]:
+    """Pop a list of serialised attributes from the attribute dictionary."""
     serialised_ = attrs.pop(serialised_items, [])
-    if not isinstance(serialised_, (list, np.ndarray)):
-        return [serialised_]
-    else:
-        return serialised_
+    return listify(serialised_)
 
 
 def _serialise(attrs: dict) -> None:
     """Convert troublesome datatypes to nicer ones in xarray attribute dictionaries.
 
     This will tackle dictionaries (to string), booleans (to int), None (to string), and sets (to list).
 
+    We also make note of any single element lists as they will be stored as simple strings in netcdf format,
+    but we want them to be returned as lists on loading the data from file.
+
     Args:
         attrs (dict):
             Attribute dictionary from an xarray Dataset/DataArray.
             Changes will be made in-place, so be sure to supply a copy of your dictionary if you want access to its original state.
     """
-    # Convert dicts attrs to yaml strings
+    # Keep track of single element lists, to listify them again when loading from file.
+
+    attrs["serialised_single_element_list"] = [
+        k for k, v in attrs.items() if isinstance(v, list) and len(v) == 1
+    ]
+
+    # Convert dict attrs to yaml strings
     dict_attrs = [k for k, v in attrs.items() if isinstance(v, dict)]
     attrs["serialised_dicts"] = dict_attrs
     for attr in dict_attrs:
@@ -89,6 +97,10 @@ def _serialise(attrs: dict) -> None:
             )
     else:
         attrs["serialised_sets"] = set_attrs
+        # Also keep track of single element sets
+        attrs["serialised_single_element_list"].extend(
+            [k for k in set_attrs if len(attrs[k]) == 1]
+        )
 
 
 def _deserialise(attrs: dict) -> None:
@@ -107,6 +119,8 @@ def _deserialise(attrs: dict) -> None:
         attrs[attr] = bool(attrs[attr])
     for attr in _pop_serialised_list(attrs, "serialised_nones"):
         attrs[attr] = None
+    for attr in _pop_serialised_list(attrs, "serialised_single_element_list"):
+        attrs[attr] = listify(attrs[attr])
     for attr in _pop_serialised_list(attrs, "serialised_sets"):
         attrs[attr] = set(attrs[attr])
 

tests/test_io.py

@@ -25,6 +25,9 @@ def model(self, vars_to_add_attrs):
             "foo_dict": {"foo": {"a": 1}},
             "foo_attrdict": calliope.AttrDict({"foo": {"a": 1}}),
             "foo_set": set(["foo", "bar"]),
+            "foo_set_1_item": set(["foo"]),
+            "foo_list": ["foo", "bar"],
+            "foo_list_1_item": ["foo"],
         }
         model._model_data = model._model_data.assign_attrs(**attrs)
         model.build()
@@ -67,6 +70,9 @@ def test_save_netcdf(self, model_file):
             ("foo_dict", dict, {"foo": {"a": 1}}),
             ("foo_attrdict", calliope.AttrDict, calliope.AttrDict({"foo": {"a": 1}})),
             ("foo_set", set, set(["foo", "bar"])),
+            ("foo_set_1_item", set, set(["foo"])),
+            ("foo_list", list, ["foo", "bar"]),
+            ("foo_list_1_item", list, ["foo"]),
         ],
     )
     @pytest.mark.parametrize("model_name", ["model", "model_from_file"])
@@ -100,7 +106,8 @@ def test_serialised_list_popped(self, request, serialised_list, model_name):
                 "serialised_dicts",
                 ["foo_dict", "foo_attrdict", "defaults", "config", "math"],
             ),
-            ("serialised_sets", ["foo_set"]),
+            ("serialised_sets", ["foo_set", "foo_set_1_item"]),
+            ("serialised_single_element_list", ["foo_list_1_item", "foo_set_1_item"]),
         ],
     )
     def test_serialisation_lists(