If you need to speed up Python, Cython is a very useful tool. It lets you seamlessly merge Python syntax with calls into C or C++ code, making it easy to write high-performance extensions with rich Python interfaces.
That being said, Cython is not the best tool in all circumstances. So in this article I’ll go over some of the limitations and problems with Cython, and suggest some alternatives.
Source: Some reasons to avoid Cython, an article by Itamar Turner-Trauring.