fix: keep dash-named parameters in netcdf round trip

doc/release_notes.rst

@@ -4,6 +4,8 @@ Release Notes
 Upcoming Version
 ----------------
 
+* ``read_netcdf`` no longer drops parameters, parameter attributes or ``MultiIndex`` dimensions whose name contains ``-``. (`#1025 <https://github.com/PyPSA/linopy/pull/1025>`__)
+
 Version 0.10.0
 --------------
 

linopy/expressions.py

@@ -1275,7 +1275,9 @@ def _add_constant_legacy(
             if is_nan_scalar(other):
                 check_user_nan()
             warn_legacy_absence(self.const)
-            return self.assign(const=self.const.fillna(0) + other)
+            return self.assign(
+                const=self.const.fillna(0) + cast("float | np.number", other)
+            )
         self_const, da, needs_reindex = self._broadcast_and_align(
             other, fill_value, join
         )

linopy/io.py

@@ -15,6 +15,7 @@
 from dataclasses import replace
 from importlib.metadata import version
 from io import BufferedWriter
+from itertools import chain
 from pathlib import Path
 from tempfile import TemporaryDirectory
 from typing import TYPE_CHECKING, Any, TypeVar
@@ -1219,7 +1220,7 @@ def read_netcdf(path: Path | str, **kwargs: Any) -> Model:
     m = Model(sparse=bool(ds.attrs.get("sparse", False)))
 
     def has_prefix(k: str, prefix: str) -> bool:
-        return k.rsplit("-", 1)[0] == prefix
+        return owner(k) == prefix
 
     def remove_prefix(k: str, prefix: str) -> str:
         return k[len(prefix) + 1 :]
@@ -1269,15 +1270,32 @@ def container_names(kind: str) -> list[str]:
             )
         return ordered
 
+    containers = {
+        kind: container_names(kind)
+        for kind in ("variables", "expressions", "constraints")
+    }
+    # Data variables and attributes are stored as ``<prefix>-<key>``, with
+    # prefix ``<kind>-<name>``, ``objective`` or ``parameters``. Names and keys
+    # (parameter names, attribute names, dimensions) may contain dashes, so a
+    # key belongs to the longest known prefix.
+    prefixes = {"objective", "parameters", *chain.from_iterable(containers.values())}
+
+    def owner(k: str) -> str | None:
+        parts = k.split("-")
+        for i in range(len(parts) - 1, 0, -1):
+            if (prefix := "-".join(parts[:i])) in prefixes:
+                return prefix
+        return None
+
     variables = {}
-    for k in container_names("variables"):
+    for k in containers["variables"]:
         name = remove_prefix(k, "variables")
         variables[name] = Variable(get_prefix(ds, k), m, name)
 
     m._variables = Variables(variables, m)
 
     expressions: dict[str, LinearExpression | QuadraticExpression] = {}
-    for k in container_names("expressions"):
+    for k in containers["expressions"]:
         name = remove_prefix(k, "expressions")
         expr_ds = get_prefix(ds, k)
         expr_type = expr_ds.attrs.pop(EXPR_TYPE_ATTR, None)
@@ -1295,7 +1313,7 @@ def container_names(kind: str) -> list[str]:
     m._expressions = Expressions(expressions, m)
 
     constraints: dict[str, ConstraintBase] = {}
-    for k in container_names("constraints"):
+    for k in containers["constraints"]:
         name = remove_prefix(k, "constraints")
         con_ds = get_prefix(ds, k)
         if con_ds.attrs.get("_linopy_format") == "csr":

test/test_io.py

@@ -360,6 +360,44 @@ def test_model_to_netcdf_with_dash_names(
     assert_model_equal(m, p)
 
 
+def test_model_to_netcdf_with_dash_named_parameters(
+    model: Model, tmp_path: Path
+) -> None:
+    m = model
+    m.parameters["my-param"] = xr.DataArray(
+        [5, 6], dims=["my-dim"], coords={"my-dim": ["a", "b"]}
+    )
+    m.parameters.attrs["my-attr"] = "kept"
+    fn = tmp_path / "test.nc"
+    m.to_netcdf(fn)
+    p = read_netcdf(fn)
+
+    assert_model_equal(m, p)
+    assert p.parameters.attrs == m.parameters.attrs
+
+
+def test_model_to_netcdf_with_dash_named_multiindex_dim(tmp_path: Path) -> None:
+    from linopy.semantics import is_v1
+
+    if is_v1():
+        pytest.skip("v1 rejects MultiIndex; this model only builds under legacy")
+    index = pd.MultiIndex.from_tuples(
+        [(1, "a"), (1, "b"), (2, "a")], names=["first", "second"]
+    )
+    coords = xr.Coordinates.from_pandas_multiindex(index, "multi-dim")
+    m = Model()
+    x = m.add_variables(coords=coords, name="x")
+    m.add_objective(x.sum())
+    m.parameters["param"] = xr.DataArray([1, 2, 3], coords=coords)
+    fn = tmp_path / "test.nc"
+    m.to_netcdf(fn)
+    p = read_netcdf(fn)
+
+    assert_model_equal(m, p)
+    for index in (p.variables["x"].indexes, p.parameters.indexes):
+        assert isinstance(index["multi-dim"], pd.MultiIndex)
+
+
 def test_model_to_netcdf_with_status_and_condition(
     model_with_dash_names: Model, tmp_path: Path
 ) -> None: