I used PLY to write a parser for a moderately complex internal language a while ago at work and it was a great experience. I ended up with very readable code. (

I used PLY to write a parser for a moderately complex internal language a while ago at work and it was a great experience. I ended up with very readable code. (And with only a little hackery I was able to write a tool to perform source code transformations while preserving comments and formatting around the changes.) I'd definitely use it again. The only potential downside is speed: it's Python, so there's only so fast it can go compared to other languages.