One of the major players in Python concurrent programming is the Global Interpreter Lock (GIL). In this chapter, we will cover the definition and purposes of the GIL, and how it affects concurrent Python applications. The problems that the GIL poses for Python concurrent systems and the controversy around its implementation will also be discussed. Finally, we will mention some thoughts on how Python programmers and developers should think about, and interact with, the GIL.

The following topics will be covered in this chapter:

• A brief introduction to the GIL: what gave rise to it, and the problems it causes
• Efforts in removing/fixing the GIL in Python
• How to effectively work with the GIL in Python concurrent programs