lex: Invalid regular expression for rule 't_POUND'. unbalanced parenthesis
lex: Make sure '#' in rule 't_POUND' is escaped with '\#'.
Traceback (most recent call last):
  File "./lex_re3.py", line 27, in <module>
    lex.lex()
  File "../ply/lex.py", line 759, in lex
    raise SyntaxError,"lex: Unable to build lexer."
SyntaxError: lex: Unable to build lexer.