Merge pull request #5274 from agriyakhetarpal/roundtrip-serialisation-fix

Don't be too strict with func_args longer than symbol.children

Author: valentinsulzer

src/pybamm/parameters/parameter_values.py

@@ -866,12 +866,21 @@ def _process_function_parameter(self, symbol):
                 else:
                     new_children.append(self.process_symbol(child))
 
-            # Get the expression and inputs for the function
+            # Get the expression and inputs for the function.
+            # func_args may include arguments that were not explicitly wired up
+            # in this FunctionParameter (e.g., kwargs with default values). After
+            # serialisation/deserialisation, we only recover the children that were
+            # actually connected.
+            #
+            # Using strict=True here therefore raises a ValueError when there are
+            # more args than children. We allow func_args to be longer than
+            # symbol.children and only build the mapping for the args for which we
+            # actually have children.
             expression = function_parameter.child
             inputs = {
                 arg: child
                 for arg, child in zip(
-                    function_parameter.func_args, symbol.children, strict=True
+                    function_parameter.func_args, symbol.children, strict=False
                 )
             }
 

tests/unit/test_parameters/test_parameter_values.py

@@ -1298,6 +1298,31 @@ def test_to_json_with_filename(self):
         finally:
             os.remove(temp_path)
 
+    def test_roundtrip_with_keyword_args(self):
+        def func_no_kwargs(x):
+            return 2 * x
+
+        def func_with_kwargs(x, y=1):
+            return 2 * x
+
+        x = pybamm.Scalar(2)
+        func_param = pybamm.FunctionParameter("func", {"x": x})
+
+        parameter_values = pybamm.ParameterValues({"func": func_no_kwargs})
+        assert parameter_values.evaluate(func_param) == 4.0
+
+        serialized = parameter_values.to_json()
+        parameter_values_loaded = pybamm.ParameterValues.from_json(serialized)
+        assert parameter_values_loaded.evaluate(func_param) == 4.0
+
+        parameter_values = pybamm.ParameterValues({"func": func_with_kwargs})
+        assert parameter_values.evaluate(func_param) == 4.0
+
+        serialized = parameter_values.to_json()
+        parameter_values_loaded = pybamm.ParameterValues.from_json(serialized)
+
+        assert parameter_values_loaded.evaluate(func_param) == 4.0
+
     def test_convert_symbols_in_dict_with_interpolator(self):
         """Test convert_symbols_in_dict with interpolator (covers lines 1154-1170)."""
         import numpy as np