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Subject: Re: Periodic execution with asyncio
From: "Tobias M." <tm@tobix.eu>
Date: Tue, 26 Nov 2013 17:35:26 +0100
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Thanks Phil, now I understand!
I wasn't aware of the fact that tasks are au=
tomatically attached to the event loop when they are created via their cons=
tructor=2E I thought I have to pass them to a run_* method explicitly=2E


=


Phil Connell <pconnell@gmail=2Ecom> schrieb:
>On Sat, Nov 23, 2013 at 09:=
30:29PM +0100, Tobias M=2E wrote:
>> Now putting this into a PeriodicTask c=
lass that provides a similar
>interface
>> like our callback version, I get=
:
>> 
>> 
>> import asyncio
>> 
>> class PeriodicTask2(object):
>> 
>>     =
 def __init__(self, func, interval):
>>          self=2Efunc =3D func
>>   =
       self=2Einterval =3D interval
>>          self=2E_loop =3D asyncio=2E=
get_event_loop()
>> 
>>      def start(self):
>>          self=2Eloop=2Erun=
_until_complete(asyncio=2ETask(self=2E_run()))
>> 
>>     @asyncio=2Ecorout=
ine
>>      def _run(self):
>>          while True:
>>                 yiel=
d from asyncio=2Esleep(self=2Einterval)
>>                 self=2Efunc()
>>=
 
>> 
>> I don't know if I misunderstood anything, but as a user of this cl=
ass
>I am
>> not able to run two task simultaneously because start() will b=
lock=2E
>In the
>> callback version I could instanciate two PeriodicTasks a=
nd run them
>both at
>> the same time (after a call to loop=2Erun_forever()=
), which is actually
>what I
>> wanted to achieve with this class=2E
>
>You=
 need to separate out creating tasks from running the event loop=2E
>
>Spec=
ifically, you should run the event loop in exactly one place,
>probably at
=
>the top level of your script=2E
>
>
>A toy example:
>
>import asyncio
>
>@=
asyncio=2Ecoroutine
>def adder(*args, delay):
>    yield from asyncio=2Esle=
ep(delay)
>    print(sum(args))
>
>def main():
>    asyncio=2ETask(adder(1,=
 2, 3, delay=3D5))
>    asyncio=2ETask(adder(10, 20, delay=3D3))
>
>    loo=
p =3D asyncio=2Eget_event_loop()
>    loop=2Erun_forever()
>
>if __name__ =
=3D=3D "__main__":
>    main()
>
>
>$ =2E/python test=2Epy
>30
>6
>
>
>Note=
 that run_forever() will block indefinitely (as the name suggests
>:)=2E Th=
is
>is generally what you'll want for a long-running server=2E
>
>If you wa=
nt do something more like:
>    - Spawn some tasks
>    - Run the event loo=
p until they're done
>    - Exit
>
>then you'll need to use loop=2Erun_unti=
l_complete(asyncio=2Egather(*tasks))
>instead=2E
>
>
>HTH,
>Phil

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<html><head></head><body>Thanks Phil, now I understand!<br>
I wasn&#39;t aw=
are of the fact that tasks are automatically attached to the event loop whe=
n they are created via their constructor=2E I thought I have to pass them t=
o a run_* method explicitly=2E<br>
<br><br><div class=3D"gmail_quote"><br>
=
<br>
Phil Connell &lt;pconnell@gmail=2Ecom&gt; schrieb:<blockquote class=3D=
"gmail_quote" style=3D"margin: 0pt 0pt 0pt 0=2E8ex; border-left: 1px solid =
rgb(204, 204, 204); padding-left: 1ex;">
<pre class=3D"k9mail">On Sat, Nov =
23, 2013 at 09:30:29PM +0100, Tobias M=2E wrote:<br /><blockquote class=3D"=
gmail_quote" style=3D"margin: 0pt 0pt 1ex 0=2E8ex; border-left: 1px solid #=
729fcf; padding-left: 1ex;">Now putting this into a PeriodicTask class that=
 provides a similar interface<br />like our callback version, I get:<br /><=
br /><br />import asyncio<br /><br />class PeriodicTask2(object):<br /><br =
/>def __init__(self, func, interval):<br />self=2Efunc =3D func<br />self=
=2Einterval =3D interval<br />self=2E_loop =3D asyncio=2Eget_event_loop()<b=
r /><br />def start(self):<br />self=2Eloop=2Erun_until_complete(asyncio=2E=
Task(self=2E_run()))<br /><br />@asyncio=2Ecoroutine<br />def _run(self):<b=
r />while True:<br />yield from asyncio=2Esleep(self=2Einterval)<br />self=
=2Efunc()<br /><br /><br />I don't know if I misunderstood anything, but as=
 a user of this class I am<br />not able to run two task simultaneously bec=
ause start() will block=2E In the<br />callback version I could instanciate=
 two PeriodicTasks and run them both at<br />the same time (after a call to=
 loop=2Erun_forever()), which is actually what I<br />wanted to achieve wit=
h this class=2E</blockquote><br />You need to separate out creating tasks f=
rom running the event loop=2E<br /><br />Specifically, you should run the e=
vent loop in exactly one place, probably at<br />the top level of your scri=
pt=2E<br /><br /><br />A toy example:<br /><br />import asyncio<br /><br />=
@asyncio=2Ecoroutine<br />def adder(*args, delay):<br />yield from asyncio=
=2Esleep(delay)<br />print(sum(args))<br /><br />def main():<br />asyncio=
=2ETask(adder(1, 2, 3, delay=3D5))<br />asyncio=2ETask(adder(10, 20, delay=
=3D3))<br /><br />loop =3D asyncio=2Eget_event_loop()<br />loop=2Erun_forev=
er()<br /><br />if __name__ =3D=3D "__main__":<br />main()<br /><br /><br /=
>$ =2E/python <a href=3D"http://test=2Epy">test=2Epy</a><br />30<br />6<br =
/><br /><br />Note that run_forever() will block indefinitely (as the name =
suggests :)=2E This<br />is generally what you'll want for a long-running s=
erver=2E<br /><br />If you want do something more like:<br />- Spawn some t=
asks<br />- Run the event loop until they're done<br />- Exit<br /><br />th=
en you'll need to use loop=2Erun_until_complete(asyncio=2Egather(*tasks))<b=
r />instead=2E<br /><br /><br />HTH,<br />Phil<br /><br /></pre></blockquot=
e></div></body></html>
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