> If they use Numpy in Python they surely use Fortran under the hood. Even that is disappearing. It was common practice even 10 years ago to use MKL as backend

> If they use Numpy in Python they surely use Fortran under the hood. Even that is disappearing. It was common practice even 10 years ago to use MKL as backend. > Did you work in HFT? Yes, I've done (and still do) HFT and mid freq since around 15 years. > I would be very surprised if they used Python for that Surprise! Nobody would dare do any heavy computation in e.g. C++ or Fortran or Cobol. It's just too unpractical, and slow to develop. You calibrate your models in Python/pandas/... , offline on historical data, and just use the prebuilt model to make the real-time prediction in C++, which doesn't involve much more than simple linear algebra. I would estimate conservatively that 80% of quants use Python, in both HFT and mid freq. There should be some niche where they use matlab, R, kdb or stata, but that's definitely a small fraction.