django - Form Wizard: Redirecting back to a previous step when validation fails -

i have implemented wizard consist of 4 forms.however need put check on variable true go next step else go previous step. inside process step:-

        def process_step(self, form):             """             can save form here,             since it's guaranteed valid             """             guest_user = false             if self.steps.current == "step1":                 step1_data = self.get_form_step_data(form)             if self.steps.current == "step2":                 step2_data = self.get_form_step_data(form)             if self.steps.current == "step3":                 step3_data = self.get_form_step_data(form)              if self.steps.current == "step4":                 step4_data = self.get_form_step_data(form)                  inv_data = check_inventory_for_cart_items(self.request)             # @ point want redirect step3                 if not inv_data[0] == true:                 messages.error(self.request, "some items out of stock. please    check in order summary")                     return               return super(singlepagecheckoutwizard, self).process_step(form) 

as can have put return , hence redirects same step template want should redirect previous step template.

thanks