Has anyone ever had code in Python, that turned out not to perform fast enough?
I mean, you were forced to choose another language because of it?
We are investigating using Python for a couple of larger projects, and my feeling is that in most cases, Python is plenty fast enough for most scenarios (compared to say, Java) because it relies on optimized C routines.
I wanted to see if people had instances where they started out in Python, but ended up having to go with something else because of performance.
Thanks.
Not so far. I work for a company that has a molecular simulation engine and a bunch of programs written in python for processing the large multi-gigabyte datasets. All of our analysis software is now being written in Python because of the huge advantages in development flexibility and time. 
If something is not fast enough we profile it with cProfile and find the bottlenecks. Usually there are one or two functions which take up 80 or 90% of the runtime. We then take those functions and rewrite them in C, something which Python makes dead easy with its C API. In many cases this results in an order of magnitude or more speedup. Problem gone. We then go on our merry way continuing to write everything else in Python. Rinse and repeat...
For entire modules or classes we tend to use Boost.python, it can be a bit of a bear but ultimately works well. If it's just a function or two, we sometimes inline it with scipy.weave if the project is already using scipy.
Python Performance - have you ever had to rewrite in something else?