That's only true if your program (a) isn't written yet, and (b) wouldn't benefit from doing things which are difficult in Python (e.g., from being even higher-level). It's not learning time -- I already know Python quite well.
I know Python-only is fine for many people, but for others it is a showstopper. I've got a bunch of Lisp code I wouldn't mind hosting on Google's servers but there's zero chance I'll ever take the time to greenspun myself macros, multimethods, parts of the MOP, various Lisp-only libraries, and so on that it uses, and then re-optimize my program for their unique architecture.
Short answers: (a) Common Lisp, typically SBCL. (b) Nothing terribly exotic about the selection, but since Lisp libs tend to be Lisp-all-the-way-down (compared to wrapper-on-a-C-lib, common in the Python world) you can use them in creative ways the authors never imagined, which would elsewhere require, say, rebuilding C code with custom hooks. (c) Not yet, but my CTO keeps bugging me to start one, so maybe next week when I have more time...
I know Python-only is fine for many people, but for others it is a showstopper. I've got a bunch of Lisp code I wouldn't mind hosting on Google's servers but there's zero chance I'll ever take the time to greenspun myself macros, multimethods, parts of the MOP, various Lisp-only libraries, and so on that it uses, and then re-optimize my program for their unique architecture.