core: better error on export of internal type

more descriptive error when trying to export OrType, NoneOr, ValueType
and DataTypeType

Change-Id: If13815e9d2b177042b24a1bb62b1ad1d1d88b502
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/32737
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Alexander Zaft <a.zaft@fz-juelich.de>

frappy/datatypes.py

@@ -90,7 +90,11 @@ class DataType(HasProperties):
 
     def export_datatype(self):
         """return a python object which after jsonifying identifies this datatype"""
-        raise NotImplementedError
+        raise ProgrammingError(
+            f"{type(self).__name__} is not able to be exported to SECoP. "
+            f"It is intended for internal use only."
+        )
+
 
     def export_value(self, value):
         """if needed, reformat value for transport"""
@@ -1232,6 +1236,7 @@ class OrType(DataType):
         self.types = types
         self.default = self.types[0].default
 
+
     def __call__(self, value):
         """accepts any of the given types, takes the first valid"""
         for t in self.types:

test/test_datatypes.py

@@ -41,7 +41,7 @@ def copytest(dt):
 
 def test_DataType():
     dt = DataType()
-    with pytest.raises(NotImplementedError):
+    with pytest.raises(ProgrammingError):
         dt.export_datatype()
     with pytest.raises(NotImplementedError):
         dt('')