code: def reset_to_flows(self, force=False, _meta=None):
          
          # Development note: The attributes which should be removed are
          # defined in self.__non_agg_attributes__
          strwarn = None
          for df in self.__basic__:
              if (getattr(self, df)) is None:
                  if force:
                      strwarn = ("Reset system warning - Recalculation after "
                                 "reset not possible "
                                 "because {} missing".format(df))
                      warnings.warn(strwarn, ResetWarning)
  
                  else:
                      raise ResetError("To few tables to recalculate the "
                                       "system after reset ({} missing) "
                                       "- reset can be forced by passing "
                                       "'force=True')".format(df))
  
          if _meta:
              _meta._add_modify("Reset to absolute flows")
              if strwarn:
                  _meta._add_modify(strwarn)
  
          [setattr(self, key, None) for key in self.__non_agg_attributes__]
          return self
docs: Keeps only the absolute values.
  
          This removes all attributes which can not be aggregated and must be
          recalculated after the aggregation.
  
          Parameters
          ----------
  
          force: boolean, optional
              If True, reset to flows although the system can not be
              recalculated. Default: False
  
          _meta: MRIOMetaData, optional
              Metadata handler for logging, optional. Internal