def def_default_identifier_token(parser, token_label='k_identifier', signed
    =True, on_ties=0):
    """Define a identifier.  It is like Python identifiers: a letter or underscore followed
    by any number of letters, underscores, and digits."""
    regex = '[a-zA-Z_][a-zA-Z0-9_]*'
    tok = parser.def_token(token_label, regex, on_ties=on_ties)
    return tok
