def __call__(self):
        if not self._initialized:
            self.init()
        return self
Returns the previous step before the given `step`. If there are no
dataset/ETHPy150Open VisTrails/VisTrails/vistrails/gui/application_server.py/VistrailsServerSingleton.__call__--crossover with--dataset/ETHPy150Open Bouke/django-two-factor-auth/two_factor/views/utils.py/IdempotentSessionWizardView.get_prev_step