Modify to multi variable constraint function

src/CSET/operators/constraints.py

@@ -63,13 +63,28 @@ def generate_var_constraint(varname: str, **kwargs) -> iris.Constraint:
 
     Returns
     -------
-    varname_constraint: iris.Constraint
+    An Iris constraint for either:
+      - a single UM STASH code
+      - a single variable name
+      - a list of variable names (Cardington multi-input case)
     """
-    if re.match(r"m[0-9]{2}s[0-9]{2}i[0-9]{3}$", varname):
-        varname_constraint = iris.AttributeConstraint(STASH=varname)
-    else:
-        varname_constraint = iris.Constraint(name=varname)
-    return varname_constraint
+    _STASH_RE = re.compile(r"m\d{2}s\d{2}i\d{3}$")
+    # ---- CASE 1: list of variable names (e.g. Cardington multi-variable) ----
+    if isinstance(varname, (list, tuple)):
+        return iris.Constraint(
+            cube_func=lambda cube: (
+                cube.long_name in varname
+                or cube.standard_name in varname
+                or cube.var_name in varname
+            )
+        )
+
+    # ---- CASE 2: single UM STASH code ----
+    if _STASH_RE.match(varname):
+        return iris.AttributeConstraint(STASH=varname)
+
+    # ---- CASE 3: single variable name ----
+    return iris.Constraint(name=varname)
 
 
 def generate_level_constraint(

tests/operators/test_constraints.py

@@ -16,6 +16,8 @@
 
 from datetime import datetime
 
+import iris
+import numpy as np
 import pytest
 
 from CSET.operators import constraints
@@ -279,6 +281,33 @@ def test_generate_attribute_constraint_with_value():
     assert expected_attr_constraint in repr(attr_constraint)
 
 
+def test_generate_var_constraint_multiple_names():
+    """Test constraint works for multiple variable names."""
+    # Create two cubes with different names
+    cube1 = iris.cube.Cube(np.arange(5), long_name="temperature_long")
+    cube1.var_name = "var_temperature"
+    cube2 = iris.cube.Cube(np.arange(5), standard_name="wind_speed")
+    # Third cube that should NOT match
+    cube3 = iris.cube.Cube(np.arange(5), long_name="surface_pressure")
+    # Generate constraint with multiple names
+    constraint = constraints.generate_var_constraint(["var_temperature", "wind_speed"])
+    # Apply constraint
+    cubes = iris.cube.CubeList([cube1, cube2, cube3])
+    result = cubes.extract(constraint)
+    # Check correct cubes are selected
+    result_names = [c.name() for c in result]
+
+    assert cube1 in result
+    assert cube2 in result
+    assert cube3 not in result
+
+    assert "temperature_long" in result_names
+    assert "wind_speed" in result_names
+    assert "surface_pressure" not in result_names
+    # Should only return 2 cubes
+    assert len(result) == 2
+
+
 def test_generate_remove_single_level_constraint():
     """Tests constraint to remove default model_level_number of zero."""
     remove_level_constraint = constraints.generate_remove_single_level_constraint(