Expert Python Programming - Third Edition

Python async and await keywords

The async and await keywords are the main building blocks in Python asynchronous programming.

The async keyword, when used before the def statement, defines a new coroutine. The execution of the coroutine function may be suspended and resumed in strictly defined circumstances. Its syntax and behavior are very similar to generators (refer to Chapter 3, Modern Syntax Elements - Below the Class Level). In fact, generators need to be used in the older versions of Python whenever you want to implement coroutines. Here is an example of function declaration that uses the async keyword:

async def async_hello(): 
    print("hello, world!") 

Functions defined with the async keyword are special. When called, they do not execute ...