docs: def _get_tnames(self):
          """Get the name of the time coordinate of the objects in this list"""
          tnames = set()
          for arr in self:
              if isinstance(arr, InteractiveList):
                  tnames.update(arr.get_tnames())
              else:
                  tnames.add(arr.psy.decoder.get_tname(
                      next(arr.psy.iter_base_variables), arr.coords))
          return tnames - {None}