Where generators can generate data from a function via yield, they can also be used to accept data if they are used on the right-hand side of the = sign in a variable assignment. This creates a coroutine.

A coroutine is a type of function that can suspend and resume execution, via yield, at predefined locations within its code. In addition to yield(), coroutines also have send() and close() functions for processing data. The send() function passes data to a coroutine (the acceptance part of the function) and close() terminates the coroutine (as there is no way for garbage collection to inherently close it for us).

Using the asyncio module allows coroutines to be used to write single-threaded, concurrent programs. As they are single-threaded, they still only perform one job but the concurrency simulates multithreading. More information about concurrency and parallel programming can be found in the next section, When to use parallel processing.