HSM ValueError improved

As mentioned in #238, the ValueError raised when an incompatible type should be added, has not been clear. Mention the requirement specifically in the error message.
pytransitions · Jul 19, 2017 · 9f7cbe3 · 9f7cbe3
1 parent 19ec2ab
commit 9f7cbe3
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/transitions/extensions/nesting.py b/transitions/extensions/nesting.py
@@ -278,7 +278,8 @@ def traverse(self, states, on_enter=None, on_exit=None,
             elif isinstance(state, NestedState):
                 tmp_states.append(state)
             else:
-                raise ValueError("%s cannot be added to the machine since its type is not known." % state)
+                raise ValueError("%s is not an instance or subclass of NestedState "
+                                 "required by HierarchicalMachine." % state)
             new_states.extend(tmp_states)
 
         duplicate_check = []