After using PLY in production and (afterwards) toying with Parsec for a side project, I could never go back to PLY. Even aside from PLY's obvious flaws (docstrings as code, mutation instead of returns, ample use of python magic backstage...), Parsec wins by being more configurabile and composable.
Whoever is maintaining my PLY mess now might get a handle on it faster than they could learn Haskell, but probably not by much.
Could you elaborate why you feel this way? I could also just vote for one or the other, but I'd like to see discussion about the relative merits of PLY or Camlp4 w.r.t. Parsec.
I can't deny part of the reason is that I'm simply more comfortable with Python.
I think my main contention was the "orders of magnitude" claim in the comment I replied to. Parsec is nice, but it's not "orders of magnitude" better than PLY or camlp4 or other parsing tools in other languages.
Python, at least, has the PLY library, which makes parsing (IMO) easier than with Parsec.
Other languages, like OCaml, also make writing parsers very easy.
Haskell with Parsec might beat C with lex/yacc, but I don't think it's that great compared to what else is available.