How to use async/await in Python 3.5?
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 olderloop = 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 fooTypeError: 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.
If you already have a loop running (with some other tasks), you can add new tasks with:
asyncio.ensure_future(foo())
otherwise you might get
The event loop is already running
error.