In this chapter, I'm going to up the game a little bit, both in terms of the concepts I'll present, and in the complexity of the code snippets I'll show you. If you don't feel up to the task, or as you are reading through you realize it is getting too difficult, feel free to skip it. You can always come back to it when you feel ready.

The plan is to take a detour from the familiar single-threaded execution paradigm, and deep dive into what can be described as concurrent execution. I will only be able to scratch the surface of this complex topic, so I won't expect you to be a master of concurrency by the time you're done reading, but I will, as usual, try to give you enough information so that you can then proceed by walking the path, so to speak.

We will learn about all the important concepts that apply to this area of programming, and I will try to show you examples coded in different styles, to give you a solid understanding of the basics of these topics. To dig deep into this challenging and interesting branch of programming, you will have to refer to the Concurrent Execution section in the Python documentation (https://docs.python.org/3.7/library/concurrency.html), and maybe supplement your knowledge by studying books on the subject.

In particular, we are going to explore the following:

• The theory behind threads and processes
• Writing multithreaded code
• Writing multiprocessing code
• Using executors to spawn threads and processes
• A brief example of programming with asyncio

Let's start by getting the theory out of the way.