Another common solution to this problem is to copy the list of callbacks
before iterating over it.
Having a simple example would be helpful here so we can experiment with
these alternate approaches.
Mike
On 10/16/2011 09:04 PM, [email protected] wrote:
> Within matplotlib.cbook.CallbackRegistry both the connect() and process()
> methods check for dead references when called. If a reference is dead it
> deletes it from the callback list.
>
> I have found a situation where this presents a problem.
>
> First, a "button_press_event" calls the process method() which begins a loop
> over all of the callback items for this event. One of these items is a dead
> reference but appears late in the list. The first callback within the loop
> creates a new connection and calls the connect method. During this connect
> call the dead reference is deleted from the callback list. Then when it gets
> back to the loop within the process method the callback no longer exists in
> the list it is iterating over and there is an error thrown when it tries to
> delete the dead reference for the second time.
>
> The problem is coordination between these two places that both could
> potentially delete a dead reference to a BoundMethodProxy. In my case,
> because one loop has started ... the attempt is made twice ... and obviously
> the second results in an error.
>
> I could put together a simple example if needed to demonstrate the error.
>
> I think the easy way to handle would be to first call a method who's job is
> only to delete dead references. Then each method could call this first
> before handling the callbacks. This would keep the intermingling of the two
> loops that both check for dead references.
>
> Another (potentially more obscure approach) could be to just wrap the delete
> with a try/except - but this suffers from not fixing a bit of a design
> problem.
>
> There are likely more approaches to solving.
>
>
>
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