code: def flip_constraint(self, twig=None, solve_for=None, **kwargs):
          
          self._kwargs_checks(kwargs, additional_allowed_keys=['check_nan'])
  
          kwargs['twig'] = twig
          redo_kwargs = deepcopy(kwargs)
          undo_kwargs = deepcopy(kwargs)
  
          changed_params = self.run_delayed_constraints()
  
          param = self.get_constraint(**kwargs)
  
          if kwargs.pop('check_nan', True) and np.any(np.isnan([p.get_value() for p in param.vars.to_list()])):
              raise ValueError("cannot flip constraint while the value of {} is nan".format([p.twig for p in param.vars.to_list() if np.isnan(p.get_value())]))
  
          if solve_for is None:
              return param
          if isinstance(solve_for, Parameter):
              solve_for = solve_for.uniquetwig
  
          redo_kwargs['solve_for'] = solve_for
          undo_kwargs['solve_for'] = param.constrained_parameter.uniquetwig
  
          logger.info("flipping constraint '{}' to solve for '{}'".format(param.uniquetwig, solve_for))
          param.flip_for(solve_for)
  
          result = self.run_constraint(uniqueid=param.uniqueid, skip_kwargs_checks=True)
  
          self._add_history(redo_func='flip_constraint',
                            redo_kwargs=redo_kwargs,
                            undo_func='flip_constraint',
                            undo_kwargs=undo_kwargs)
  
          return param
docs: Flip an existing constraint to solve for a different parameter
  
          :parameter str twig: twig to filter the constraint
          :parameter solve_for: twig or actual parameter object of the new
              parameter which this constraint should constraint (solve for).
          :type solve_for: str or :class:`phoebe.parameters.parameters.Parameter
          :parameter **kwargs: any other tags to do the filter
              (except twig or context)