code: def pre_process(self, x0, params=()):
          
          # Should be used by all methods matching "solve_*"
          if self.x_by_name and isinstance(x0, dict):
              x0 = [x0[k] for k in self.names]
          if self.par_by_name and isinstance(params, dict):
              params = [params[k] for k in self.param_names]
          for pre_processor in self.pre_processors:
              x0, params = pre_processor(x0, params)
          return x0, np.atleast_1d(params)
docs: Used internally for transformation of variables.