./lex_ignore.py:20: Rule 't_ignore' must be defined as a string.
Traceback (most recent call last):
  File "./lex_ignore.py", line 29, in <module>
    lex.lex()
  File "../ply/lex.py", line 772, in lex
    raise SyntaxError,"lex: Unable to build lexer."
SyntaxError: lex: Unable to build lexer.