his chapter covers the principles of asynchronous programming and the AsyncIO library. It is composed of three parts. The first one explains what asynchronous programming is, how it is different from synchronous programming, and why and when it is more efficient than synchronous programming. This first part also goes through the history of asynchronous programming in Python to allow you to better understand the current state of Python in this domain. The second part is dedicated to the AsyncIO library. AsyncIO, the official Python asynchronous library, contains all features needed to implement readable asynchronous code. The last part explains how to implement a real application and, more specifically, an HTTP server. By the end of this chapter, you will be able to write an asynchronous network service with AsyncIO.

The following topics will be covered in this chapter:

• Asynchronous programming
• The history of asynchronous programming in Python
• An introduction to AsyncIO
• Reactive HTTP echo servers