Returns True if no errors are thrown for the specified state.

def is_valid(self, *states):
        """Returns True if no errors are thrown for the specified state."""

        # if no state is specified, fallback to the base Form's is_valid
        if not states:
            return super(StateValidatorFormMixin, self).is_valid()

        return all(self.state_validators[state].is_valid(self)
                   for state in states)