Calling out to c "because you want performance" is only only one dimension of the issue, and assumes that your main application code is written in python or julia. In many cases (e.g., robotics), application code is written in c++ or c, and python bindings serve as simulation harnesses and visualization tools. Pybind11 is absolutely brilliant for this. The last time I looked, similar tooling for Julia was substantially less mature and definitely didn't look like something I'd want integrated into a production workflow.