problem using asyncio

[AJAY AJITH]

hi, Im a beginner in asyncio. I was trying out some small scripts to bet the basic idea of asyncio. The below script is meant to print "hello" after some time period "after" is expired. But i have a strange output when i dont use asyncio.wait() inside run_until_complete().


code 1 :

    async def say_hello(after):
    await asyncio.sleep(after)
    print('hello  {0}'.format(after),end='--\n')


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    a = count()
    coros = []
    tasks = []
    for i in range(10):
        #coros.append(say_hello(i))
        tasks.append(asyncio.ensure_

future(say_hello(i)))
    tasks = asyncio.wait(tasks)
    loop.run_until_complete(tasks)

output

hello  0--
hello  1--
hello  2--
hello  3--
hello  4--
hello  5--
hello  6--
hello  7--
hello  8--
hello  9--

this works as intended.

code 2:
    async def say_hello(after):
    await asyncio.sleep(after)
    print('hello  {0}'.format(after),end='--\n')


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    a = count()
    coros = []
    tasks = []
    for i in range(10):
        #coros.append(say_hello(i))
        tasks.append(asyncio.ensure_future(say_hello(i)))
    #tasks = asyncio.wait(tasks)
    loop.run_until_complete(tasks[6])

output

hello  0--
hello  1--
hello  2--
hello  3--
hello  4--
hello  5--
hello  6--

why did it give such an output?

[Idan Haim Shalom]

Hi,

In code 2 you only wait for tasks[6] to be complete and then your program finish

that is why the program prints until hello 6-- and exit change it to the last task 9 and you will see all the output.

you can use the loop.run_forever() but then your program will never quit until you will close the loop.

That why you need the asyncio.wait(tasks) 

https://python.readthedocs.io/en/stable/library/asyncio-task.html#asyncio.wait read this