Live trading systems are in C++ or Java, but like others have said Python is used for day-to-day research, sometimes R if the particular quant likes it. I neve

Live trading systems are in C++ or Java, but like others have said Python is used for day-to-day research, sometimes R if the particular quant likes it. I never saw any Fortran in my time at Bloomberg in the 2010s but allegedly there was still a lot of it running in the nether regions.