Lex and Yacc implementation for Python2

 PLY is yet another implementation of lex and yacc for
 Python. Although several other parsing tools are available for
 Python, there are several reasons why you might want to take a look
 at PLY:
  * It's implemented entirely in Python.
  * It uses LR-parsing which is reasonably efficient and well suited
    for larger grammars.
  * PLY provides most of the standard lex/yacc features including
    support for empty productions, precedence rules, error recovery,
    and support for ambiguous grammars.
  * PLY is extremely easy to use and provides very extensive error
    checking.