Re: python classes and signal connects

[Simon Feltman <s feltman gmail com>]

Hi Thomas,

It would help to give some context as to what you are trying to
accomplish with having a class. In the example the TestSignals class
is superfluous "t = TestSignals()" could be replaced with the contents
of __init__ and the callback could be moved out as a standalone
function. But I gather what you are actually trying to do is more
complex than this?

The specific issue you are seeing is because the callback connected to
the signal is a bound method: "self.button_clicked_cb". A bound method
will keep a reference to the instance of its class TestSignals and the
function. This can be observed as follows:

test = TestSignals()
test.button_clicked_cb.__self__ == test  # True

If button_clicked_cb does not access any state on the TestSignals
instance, than by all means it should be moved outside of the class or
made into a staticmethod or classmethod.

-Simon

On Sat, Sep 29, 2012 at 3:32 AM, Thomas Bechtold
<thomasbechtold jpberlin de> wrote:
>
> Hi,
>
> I created a python (new style) class which contains a Gtk.Button and a
> callback function which is connected to the "clicked" signal:
>
> class TestSignals(object):
>     def __del__(self):
>         print "Deleted object"
>
>     def __init__(self):
>         self.button = Gtk.Button("My Button")
>         self.button.connect("clicked", self.button_clicked_cb)
>
>     def button_clicked_cb(self, button, user_data):
>         print "button clicked"
>
>
>
> When I create instances of this class in a loop, the objects are never
> destroyed (I never see "Deleted object" on the terminal and the memory
> consumption increase):
>
> if __name__ == "__main__":
>     gc.collect()
>
>     for i in range(0, 500):
>         t = TestSignals()
>         gc.collect()
>
>     print "instance generation finished (count: %s)" % (i)
>     gc.collect()
>     raw_input("press enter to exit ...")
>
>
> I can move the button_clicked_cb() function outside of the class (and
> remove the "self" parameter) and then the instances will be destroyed.
>
> Is this the correct way to handle this? Or is there something wrong with
> pyi? Imho the callback should be inside of the class.
>
>
> Cheers,
>
>
> Tom
>
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