code: def allowed_classes(self):
          
          data = clips.data.DataObject(self._env)
  
          lib.EnvSlotAllowedClasses(
              self._env, self._cls, self._name, data.byref)
  
          if isinstance(data.value, list):
              for klass in classes(self._env, data.value):
                  yield klass
docs: Iterate over the allowed classes for this slot.
  
          The Python equivalent of the CLIPS slot-allowed-classes function.