How to use async/await in python 3.5+

Question

I was trying to explain an example of async programming in python but I failed. Here is my code.

import asyncio
import time

async def asyncfoo(t):
    time.sleep(t)
    print("asyncFoo")


loop = asyncio.get_event_loop()
loop.run_until_complete(asyncfoo(10)) # I think Here is the problem
print("Foo")
loop.close()

My expectation is that I would see:

Foo
asyncFoo

With a wait of 10s before asyncFoo was displayed.

But instead I got nothing for 10s, and then they both displayed.

What am I doing wrong, and how can I explain it?

Answer 1

run_until_complete will block until asyncfoo is done. Instead, you would need two coroutines executed in the loop. Use asyncio.gather to easily start more than one coroutine with run_until_complete.

Here is a an example:

import asyncio


async def async_foo():
    print("asyncFoo1")
    await asyncio.sleep(3)
    print("asyncFoo2")


async def async_bar():
    print("asyncBar1")
    await asyncio.sleep(1)
    print("asyncBar2")


loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.gather(async_foo(), async_bar()))
loop.close()