So what should we do instead. It's very simple:
Ask him what he means. ; interrogate him:
"Why do you feel that Python is so bad? What do you find wrong with it?"
Agree with him (but use a softer language):
"Yes, Perl is a nice language, and I agree that Python has its downsides and/or trade-offs in comparison to Perl."
"It's OK to prefer Perl, we'll still accept you here."
This will make the troll lose steam and help you find a common ground.
And eventually negotiate a common ground: "Would you agree that some people like Perl better and some like Python better? (And some may like both equally.). Maybe you can still write Python code and be productive in it while still not in love with it. Who knows, maybe you'll even grow to like it. Feel free to stick around and ask questions."