code: def queryables(self):
          
  
          # compute the values_axes queryables
          return dict(
              [(a.cname, a) for a in self.index_axes] +
              [(self.storage_obj_type._AXIS_NAMES[axis], None)
               for axis, values in self.non_index_axes] +
              [(v.cname, v) for v in self.values_axes
               if v.name in set(self.data_columns)]
          )
docs: return a dict of the kinds allowable columns for this object