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Re: Design thought for callbacks

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On Feb 22, 2015, at 7:52 AM, Laura Creighton <lac@openend.se> wrote:

> In a message of Sun, 22 Feb 2015 07:16:14 -0500, Cem Karan writes:
> 
>> This was PRECISELY the situation I was thinking about.  My hope was
>> to make the callback mechanism slightly less surprising by allowing
>> the user to track them, releasing them when they aren't needed
>> without having to figure out where the callbacks were registered.
>> However, it appears I'm making things more surprising rather than
>> less.
> 
> You may be able to accomplish your goal by using a Queue with a
> producer/consumer model.
> see: http://stackoverflow.com/questions/9968592/turn-functions-with-a-callback-into-python-generators
> 
> especially the bottom of that.
> 
> I haven't run the code, but it looks mostly reasonable, except that
> you do not want to rely on the Queue maxsize being 1 here, and
> indeed, I almost always want a bigger Queue  in any case.  Use
> Queue.task_done if blocking the producer features in your design.
> 
> The problem that you are up against is that callbacks are inherantly
> confusing, even to programmers who are learning about them for the
> first time.  They don't fit people's internal model of 'how code works'.
> There isn't a whole lot one can do about that except to
> try to make the magic do as little as possible, so that more of the
> code works 'the way people expect'.

I think what you're suggesting is that library users register a Queue instead of a callback, correct?  The problem is that I'll then have a strong reference to the Queue, which means I'll be pumping events into it after the user code has gone away.  I was hoping to solve the problem of forgotten registrations in the library.

Thanks,
Cem Karan

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Re: Design thought for callbacks "Frank Millman" <frank@chagford.com> - 2015-02-21 07:41 +0200
  Re: Design thought for callbacks Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-22 03:15 +1100
    Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-21 19:08 +0200
      Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-22 07:16 -0500
        Re: Design thought for callbacks Marko Rauhamaa <marko@pacujo.net> - 2015-02-22 14:46 +0200
          Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-22 09:17 -0500
      Re: Design thought for callbacks Laura Creighton <lac@openend.se> - 2015-02-22 13:52 +0100
      Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-22 09:10 -0500
    Re: Design thought for callbacks "Frank Millman" <frank@chagford.com> - 2015-02-22 08:44 +0200
      Re: Design thought for callbacks Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-02-22 23:15 +1300
        Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-22 09:22 -0500
          Re: Design thought for callbacks Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-02-24 18:45 +1300
            Re: Design thought for callbacks Cem Karan <cfkaran2@gmail.com> - 2015-02-24 06:06 -0500
        Re: Design thought for callbacks Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-22 23:57 -0700

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