In this talk we'll explore different options for interacting with non-Python code from Python, starting with invoking an external process using the subprocess module and ending with integrating external C libraries. We'll discuss tradeoffs encountered when building systems along the way. ** "subprocess" behind the scenes ** There's a whole lot going on when you invoke another process with the functions available from the subprocess module. The Python API is simple, but it turns out that there's a whole lot going on underneath the hood when you call out to another process, and a lot of these details are important to debugging and addressing performance issues. We'll deep dive down into what's going on here and learn about the interface between userspace applications and the Linux kernel. ** wrapping C library code ** With C libraries, we have the option of more tightly integrating with a Python program, which offers us more performance and control than shelling out. We'll learn what a Foreign Function Interface is, and take a look at the different options for integrating C libraries, including ctypes, Cython, and cffi. We'll discuss the pros and cons of these options and make some recommendations for which to use when. You'll leave this talk with a better understanding of how Unix processes work, knowledge of the options available for integrating C with Python, and perhaps some inspiration on how to use the tools available to you to gain an understanding of a system when you just don't know what's going on. A reading knowledge of C will be useful but not required.