esrftaskgraph: better check for required positional Task inputs

esrftaskgraph/esrftaskgraph/task.py

@@ -40,6 +40,14 @@ class Task(Registered, hashing.UniversalHashable, register=False):
         if missing_required:
             raise ValueError(f"Missing inputs for {type(self)}: {missing_required}")
 
+        # Check required positional inputs
+        nrequiredargs = self._N_REQUIRED_POSITIONAL_INPUTS
+        for i in range(nrequiredargs):
+            if i not in inputs and str(i) not in inputs:
+                raise ValueError(
+                    f"Missing inputs for {type(self)}: positional argument #{i}"
+                )
+
         # Init missing optional inputs
         missing_optional = set(self._OPTIONAL_INPUT_NAMES) - set(inputs.keys())
         for name in missing_optional:
@@ -54,13 +62,6 @@ class Task(Registered, hashing.UniversalHashable, register=False):
         # The output hash will update dynamically if any of the input
         # variables change
         self._inputs = VariableContainer(value=inputs, varinfo=varinfo)
-        nargs = self._inputs.n_positional_variables
-        nrequiredargs = self._N_REQUIRED_POSITIONAL_INPUTS
-        if nargs < nrequiredargs:
-            raise ValueError(
-                f"Missing positional inputs for {type(self)}: {nrequiredargs} required but only {nargs} provided"
-            )
-
         self._outputs = VariableContainer(
             value=ovars,
             uhash=self._inputs,