Tkinter wart: bug or feature?

[Chad Netzer]

On Saturday 16 November 2002 06:57, Fredrik Lundh wrote:

>     lbl = Tkinter.Label(win.window, image=image1)
>     lbl.photo = image1
>
> which guarantees that the image won't be collected before
> the widget itself.

Well, maybe I need more schooling.  Could someone look at this code and tell 
me where my reasoning goes wrong.:


import Tkinter

def make_photo_label( parent ):
    image2 = Tkinter.Image('photo', file="WatchmenLogo.gif")
    lbl2 = Tkinter.Label(parent, image=image2)
    lbl2.photo = image2
    lbl2.pack(expand=1, fill=Tkinter.BOTH)
    return

if __name__ == '__main__':
    root = Tkinter.Tk()

    make_photo_label( root )

     root.mainloop()


When make_photo_label() finishes execution, the 'lbl2' variable goes out of 
scope, and is deleted from the local namespace.  So the Tkinter.Label object 
should be 'collected' (which DOESN'T mean that Tk forgets it; the widget is 
still packed, and still exists to Tk).

When 'lbl2' is collected, the reference count of 'image2' drops.  (?) 
Furthermore, when 'image2' it goes out of scope, it drops again.  So it 
should (seemingly) be collected as well, and the image should become blank.

I guess I don't understand how attaching image2 as an attribute to lbl2 
should change anything.  lbl2 still gets collected when the function is over, 
and in doing so, it's link to 'image2' should be broken, and then 'image2' 
should be collected.

However, when running the program, I see that is NOT the case.  The image 
only disappears if I comment out "bl2.photo = image2".  Do I misunderstand 
reference counting?

-- 
Bay Area Python Interest Group - http://www.baypiggies.net/

Chad Netzer
cnetzer at mail.arc.nasa.gov