#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import time
async def foo():
await time.sleep(1)
foo()
I couldn't make this dead simple example to run:
RuntimeWarning: coroutine 'foo' was never awaited foo()
Running coroutines requires an event loop. Use the asyncio()
library to create one:
import asyncio
# Python 3.7+
asyncio.run(foo())
or
# Python 3.6 and older
loop = asyncio.get_event_loop()
loop.run_until_complete(foo())
Also see the Tasks and Coroutines chapter of the asyncio
documentation. If you already have a loop running, you'd want to run additional coroutines concurrently by creating a task (asyncio.create_task(...)
in Python 3.7+, asyncio.ensure_future(...)
in older versions).
Note however that time.sleep()
is not an awaitable object. It returns None
so you get an exception after 1 second:
>>> asyncio.run(foo())
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/.../lib/python3.7/asyncio/runners.py", line 43, in run
return loop.run_until_complete(main)
File "/.../lib/python3.7/asyncio/base_events.py", line 573, in run_until_complete
return future.result()
File "<stdin>", line 2, in foo
TypeError: object NoneType can't be used in 'await' expression
In this case you should use the asyncio.sleep()
coroutine instead:
async def foo():
await asyncio.sleep(1)
which is cooperates with the loop to enable other tasks to run. For blocking code from third-party libraries that do not have asyncio equivalents, you could run that code in an executor pool. See Running Blocking Code in the asyncio development guide.