Force boolean evaluation of guards/contracts

sismic/code/python.py

@@ -65,7 +65,8 @@ class PythonEvaluator(Evaluator):
         - A *setdefault(name:str, value: Any) -> Any* function that defines and returns variable *name* in
           the global scope if it is not yet defined.
     - On guard or contract evaluation:
-        - If the code is related to a transition, the *event: Event* that fires the transition is exposed.          
+        - If the code is related to a transition, an *event: Optional[Event]* variable is exposed. This variable
+          contains the currently considered event, or None. 
     - On guard or contract (except preconditions) evaluation:
         - An *after(sec: float) -> bool* Boolean function that returns *True* if and only if the source state
           was entered more than *sec* seconds ago. The time is evaluated according to Interpreter's clock.
@@ -138,7 +139,7 @@ def _evaluate_code(self, code: Optional[str], *, additional_context: Mapping[str
         exposed_context.update(additional_context if additional_context is not None else {})
 
         try:
-            return eval(compiled_code, exposed_context, self._context)  # type: ignore
+            return bool(eval(compiled_code, exposed_context, self._context))
         except Exception as e:
             raise CodeEvaluationError('"{}" occurred while evaluating "{}"'.format(e, code)) from e
 

sismic/model/events.py

@@ -11,7 +11,7 @@ class Event:
     The list of parameters can be obtained using *dir(event)*. Notice that
     *name* and *data* are reserved names. If a *delay* parameter is provided,
     then this event will be considered as a delayed event (and won't be
-    executed until delay has elapsed).
+    executed until given delay has elapsed).
 
     When two events are compared, they are considered equal if their names
     and their data are equal.

tests/test_code.py

@@ -63,6 +63,9 @@ def test_condition_on_event(self, evaluator):
         assert evaluator._evaluate_code('event.data[\'a\'] == 1', additional_context={'event': Event('test', a=1)})
         assert evaluator._evaluate_code('event.name == \'test\'', additional_context={'event': Event('test')})
 
+        assert evaluator._evaluate_code('event', additional_context={'event': Event('a')}) is True
+        assert evaluator._evaluate_code('not event', additional_context={'event': None}) is True
+
     def test_setdefault(self, evaluator):
         evaluator._execute_code('setdefault("x", 2)')
         assert evaluator.context['x'] == 1

tests/test_model.py

@@ -13,6 +13,10 @@ def test_empty_event(self):
         with pytest.raises(TypeError):
             Event()
 
+    def test_truth_value(self):
+        assert bool(Event('a'))
+        assert (not Event('a')) is False
+
     def test_parametrized_events(self):
         event = Event('test', a=1, b=2, c=3)