Python Lex & Yacc
PLY is yet another implementation of lex and yacc for Python. Some notable features include the fact that its implemented entirely in Python and it uses LALR(1) parsing which is 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.