Combine awaitables like Promise.all
The equivalent would be using asyncio.gather
:
import asyncio
async def bar(i):
print('started', i)
await asyncio.sleep(1)
print('finished', i)
async def main():
await asyncio.gather(*[bar(i) for i in range(10)])
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
loop.close()
Why doesn't my approach work?
Because when you await
each item in seq
, you block that coroutine. So in essence, you have synchronous code masquerading as async. If you really wanted to, you could implement your own version of asyncio.gather
using loop.create_task
or asyncio.ensure_future
.
EDIT
The original answer used the lower-level asyncio.wait
.
I noticed that asyncio.gather() may be a better way to await other than asyncio.wait() if we want ordered results.
As the docs indicates, the order of result values from asyncio.gather() method corresponds to the order of awaitables in aws. However, the order of result values from asyncio.wait() won't do the same thing.You can test it.
https://docs.python.org/3/library/asyncio-task.html#asyncio.gather
asyncio.gather()
will return the list of output from each async function calls.
import asyncio
async def bar(i):
print('started', i)
await asyncio.sleep(1)
print('finished', i)
return i
async def main():
values = await asyncio.gather(*[bar(i) for i in range(10)])
print(values)
asyncio.run(main())
This method, gather, takes arbitrary number of args for the concurrent jobs instead of a list, so we unpack.
It's very common to need this intermediate value, values
in my eg, instead of designing your function/method to have side effects.