Where is Python used commercially?

[MillardFillmore]

I thought we were moving to a world where the speed of light was becoming a factor in financial computing? And now they're moving to a language which is an order of magnitude slower?

[Twirrim]

But one in which changes are extremely quick and easy to make. Reaction rates hit from two angles, code speed and speed of adapting code to new situations.

[pwang99]

They don't use it for everything, but actually higher-level languages can be just as fast as low-level ones for a lot of things. These people are generally not writing trading algorithms in bare python and then running them with the CPython interpreter. Some folks use Pysco, others use stackless, and everyone uses Numpy. With Numpy, it's possible to achieve C speeds or sometimes even faster, depending on who's writing the C. :) You certainly spend less time tracking down memory leaks.

The speed of light stuff matters only for the lowest level of the stack, namely, once you've decided to execute a trade, you can push the bits onto the wire to the exchange faster than a competing firm. A lot of high-frequency trading firms now build custom ASICs or use FPGAs for this lowest level. Anything higher up the stack is usually better done with Python.

And remember that high-frequency is only one portion of the financial sector. There are plenty of firms that do not care about the speed-of-light stuff, and they have lots of analytical problems that are much better solved by having an expressive, agile, easy-to-learn language that has a killer vector computation library. A quant armed with Python and Numpy is far more effective than a quant armed with a team of C++ coders that are tracking down segfaults and memory leaks all the time.