Is the given private key bundle a single-sig key bundle?

def is_singlesig(privkey_info, blockchain='bitcoin', **blockchain_opts):
    """
    Is the given private key bundle a single-sig key bundle?
    """
    if blockchain == 'bitcoin':
        return btc_is_singlesig(privkey_info, **blockchain_opts)
    else:
        raise ValueError('Unknown blockchain "{}"'.format(blockchain))