Design thought for callbacks

[Laura Creighton]

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'.

Laura