I had been doing PHP for years, and had only recently picked up Python. I knew Mozilla was moving sites from PHP to Python. In one on-site interview, I answered the question with Python which made it much harder than it should have been. After that interview, I erased the white-board and code on my computer. The next interviewer asked what the previous interviewer had asked me. When I told him, I told him it took me longer in Python. He gave me a chance to do it all over again now that it was fresh in my mind. Took 5 minutes the 2nd time.