It depends on what you're doing. If you load some data, process it with some Numpy routines (where speed-critical parts are implemented in C) and save a result, you can probably be almost as fast as C++... however if you write your algorithm fully in Python, you might have much worse results than being 10x slower. See for example: https://shvbsle.in/computers-are-fast-but-you-dont-know-it-p... (here they have ~4x speedup from good Python to unoptimized C++, and ~1000x from heavy Python to optimized one...)
