Modern Python Standard Library Cookbook

How to do it...

In Python, coroutines are implemented through the async def syntax and are executed through an asyncio event loop.

For example, we might write a function that runs two coroutines that count down from a given number of seconds, printing their progress. That would easily allow us to see that the two coroutines are running concurrently, as we would see output from one interleaved with output from the other:

import asyncio

async def countdown(identifier, n):
    while n > 0:
        print('left:', n, '({})'.format(identifier))
        await asyncio.sleep(1)
        n -= 1

async def main():
    await asyncio.wait([
        countdown("A", 2),
        countdown("B", 3)
    ])

Once an event loop is created and we run main within it, we will see the two functions running:

>>> loop ...