[Python-ideas] Fwd: standard library proposal for "tasklets" using generators

[Brett Cannon]

On Wed, Jan 21, 2009 at 02:45, Guillaume Chereau <charlie137 at gmail.com> wrote:
> Just realized i clicked "reply" instead of 'reply to all"
>
>
> ---------- Forwarded message ----------
> From: Guillaume Chereau <charlie137 at gmail.com>
> Date: Wed, Jan 21, 2009 at 12:00 PM
> Subject: Re: [Python-ideas] standard library proposal for "tasklets"
> using  generators
> To: Guido van Rossum <guido at python.org>
>
>
> Thanks for the answer,
>
> I understand the concern here.
>
> I still think having such a library, if not as a standard python lib,
> but at least as an independent one, that could then be used by all the
> project using such pattern (twisted, kiwi, gobject, etc.) would be a
> good idea.
> I will try to contact those different projects for suggestions.
>

If the package really takes off and it turns out there is a good
design that leads to clean code this can be re-evaluated. But getting
a third-party library out there that has wide usage is a good first
step.

-Brett



> I also have to say one of my secret hope was that the pypy interpreter
> could eventually understand this kind of 'tasklet' generators and
> generate C or other language code out of it, since pypy already has
> support for tasklets, but using a syntax that can't be interpreted by
> cpython.
>
> - Guillaume
>
> On Wed, Jan 21, 2009 at 10:56 AM, Guido van Rossum <guido at python.org> wrote:
>> The pattern of invoking all sorts of stuff that may wait indefinitely
>> using yield has been proposed before, but I find it creates rather
>> awkward code compared to using plain threads. Not something I'd like
>> to encourage by having standard decorators and other APIs around this
>> idea. I believe Twisted has something like this, and that's probably a
>> good place to isolate such patterns; in their case they really
>> want/need this, so they put up with the awkwardness. Putting the
>> necessary decorators/APIs in the language doesn't do much about the
>> awkwardness, so I don't think we should do this.
>>
>> On Tue, Jan 20, 2009 at 6:36 PM, Guillaume Chereau <charlie137 at gmail.com> wrote:
>>> Hello,
>>> Thanks to the introduction of new generator features, as described in
>>> PEP 0342, it is possible to write what I would call "tasklet" (I am no
>>> sure what should be the term exactly).
>>> tasklet are a way to write callback based code that looks like thread. Example :
>>>
>>> (assuming we have a function sleep(sec, callback) that will call the
>>> callback after `sec` seconds)
>>>
>>> @tasklet
>>> task1():
>>>    print "sleep"
>>>    yield Wait(sleep, 5)
>>>    print "called after sleep"
>>>    yield 10 # returned value
>>>
>>> @tasklet
>>> task2():
>>>    for i in range(10):
>>>        value = yield task1()
>>>
>>> (the same thing using callback only would be quite difficult to read)
>>>
>>> The library should provide -the names are not very important- a
>>> Tasklet class, plus a tasklet decorator to turn any generator into a
>>> tasklet, plus a Wait function to turn a callback function into a
>>> tasklet, plus maybe a few other functions.
>>>
>>> In many cases this kind of library would be very useful. I am
>>> currently using something very similar for a project I am working on
>>> [0]. the kiwi project also have a similar library [1] (but the syntax
>>> is not really nice because they don't take advantage of the PEP 0342
>>> features.)
>>>
>>> I guess more and more people may try to use similar library in the
>>> future, but the problem is that the implementation of it is really not
>>> trivial, so I would like to suggest having such a library in the
>>> standard set of python libraries.
>>>
>>> Do you think this is a good idea ?
>>>
>>> cheers,
>>>
>>> Guillaume
>>>
>>> [0] http://git.openmoko.org/?p=tichy.git;a=blob;f=tichy/tasklet.py
>>> [1] http://www.async.com.br/projects/kiwi/api/kiwi.tasklet.html
>>>
>>> --
>>> http://charlie137.blogspot.com/
>>> _______________________________________________
>>> Python-ideas mailing list
>>> Python-ideas at python.org
>>> http://mail.python.org/mailman/listinfo/python-ideas
>>>
>>
>>
>>
>> --
>> --Guido van Rossum (home page: http://www.python.org/~guido/)
>>
>
>
>
> --
> http://charlie137.blogspot.com/
>
>
>
> --
> http://charlie137.blogspot.com/
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> http://mail.python.org/mailman/listinfo/python-ideas
>