code: def _get_variables(self):
          
          if self._specs_in[_VARIABLES_STR] == 'all':
              return _get_all_objs_of_type(
                  Var, getattr(self._obj_lib, 'variables', self._obj_lib)
              )
          else:
              return set(self._specs_in[_VARIABLES_STR])
docs: Get the requested variables.