def get_prev_step(self, step=None):
        if step is None:
            step = self.steps.current
        form_list = self.get_form_list()
        keys = list(form_list.keys())
        key = keys.index(step) - 1
        if key >= 0:
            for prev_step in keys[key::-1]:
                if self.is_step_visible(prev_step):
                    return prev_step
        return None
Function to return the right hand side for the system.
dataset/ETHPy150Open Bouke/django-two-factor-auth/two_factor/views/utils.py/IdempotentSessionWizardView.get_prev_step--crossover with--dataset/ETHPy150Open simpeg/simpeg/SimPEG/MT/Problem1D/Probs.py/eForm_TotalField.getRHS