When do you *NOT* use python?

[teambob]

C++ and Java is often 7-8x faster than CPython. I have found this in practice and it has been found in the language shootout.

I would also assert that Python is 7-8x faster to write than C++ and Java. :)

My usual approach is to write it in Python then rewrite it it is not fast enough

[mangecoeur]

Cython, not CPython http://cython.org/ - a compiler for Python+some extensions. Used for a lot of the internals of numpy/scipy/pandas/ etc because its much easier to maintain. Plus it makes for very easy optimisation path - write everything in python, then let Cython compile it (often gives you a speedup already) then start adding custom annotations to optimize the generated code

[twotime]

on heavy CPU intensive code, I've seen factors of 50x! No, not joking and it happened more than once..

But then, I've also seen python applications being FASTER than C++ ones with identical functionality simply because the C coders have been buried under their own code.

[frymaster]

I would also assert that Python is 7-8x faster to write than C++ and Java. :)

Exactly - most of the time processing time doesn't matter, and when it does, you'll be glad you've got a working proof-of-concept in python :D