When someone finds Python slow, Cython is a popular choice to speed it up. But how slow is any given thing you’re doing? How much faster is Cython? 100X of what? In this talk, we will write some python data analysis code in Cython, read some parts of its generated code to understand what all Python has to do to run it, and understand how long different things take by running microbenchmarks. We will then see how simple hints to Cython can help it generate faster code, and see how fast it gets. This talk is intended for Python users writing performance sensitive applications, who are at least mildly familiar with Cython and/or C/C++. Attendees will learn how to profile and optimize common operations, which should help them to evaluate Cython or Python for their use-case.