def skymapweights_keys(self):
    """
    Return the list of string names of valid weight attributes.  For unpolarized
    weights, this list includes only TT.  Otherwise, the list includes all six
    unique weight attributes in row major order: TT, TQ, TU, QQ, QU, UU.
    """
    if self.polarized:
        return ['TT', 'TQ', 'TU', 'QQ', 'QU', 'UU']
    return ['TT']