I have helped plenty of people solve problems in languages I don't know. I would not suggest that this makes me an expert or even all that unusual. However, I suspect that a great C++ programmer would be more useful to a Python project than an average Python programmer in about 3 weeks.
Is the person who hires you willing to risk their reputation or job that a C++ programmer can do the job when there may be other Python programmers out there?
I have never gotten a job because I was a specialist in the specific language they wanted. From what I have seen the most important questions are can the program and will they flake out. After that it's just a question of how well they fit into the team.
PS: Outside of a tiny startup few people really risk much with any given new hire.
