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.
This kind of question is likely to start a religious war among language people so let me answer it a little bit differently.
For most cases in today's computing environments your choice of programming language should be based on what you can program efficiently, program well and what makes you happy not the performance characteristics of the language. Also, optimization should generally be the last concern when programming any system. 
The typical python way to do things is to start out writing your program in python and then if you notice the performance suffering profile the application and attempt to optimize the hot-spots in python first. If optimizing the python code still isn't good enough the areas of the code that are weighing you down should be re-written as a python module in C. If even after all of that your program isn't fast enough you can either change languages or look at scaling up in hardware or concurrency.
That's the long answer, to answer your question directly; no, python (sometimes with C extensions) has been fast enough for everything I need it to do. The only time I really dip into C is to get access to stuff that donesn't have python bindings.
Edit: My background is a python programmer at a large .com where we use python for everything from the front-end of our websites all the way down to all the back-office systems. Python is very much an enterprise-grade language.
Python Performance - have you ever had to rewrite in something else?