code: def _sel_var(ds, var, upcast_float32=True):
      
      for name in var.names:
          try:
              da = ds[name].rename(var.name)
              if upcast_float32:
                  return _maybe_cast_to_float64(da)
              else:
                  return da
          except KeyError:
              pass
      msg = '{0} not found among names: {1} in\n{2}'.format(var, var.names, ds)
      raise LookupError(msg)
docs: Select the specified variable by trying all possible alternative names.
  
      Parameters
      ----------
      ds : Dataset
          Dataset possibly containing var
      var : aospy.Var
          Variable to find data for
      upcast_float32 : bool (default True)
          Whether to cast a float32 DataArray up to float64
  
      Returns
      -------
      DataArray
  
      Raises
      ------
      KeyError
          If the variable is not in the Dataset