Fwd: Tkinter: image handling: bug or feature?

[Jose' Sebrosa]

johngrayson at home.com wrote:
> 
> --- In python-list at y..., Jose' Sebrosa <sebrosa at a...> wrote:
> 
> >> Hi,
> >>
> >> I just figured out that this code
> >>
> >> I like to use local names to everything I can (so the names are not
> >>available when mainloop is called)
> >>
> >> Or I'm simplly messing it all...
> 
> Yes, you're messing it up...   :-)
> 
> If you insist on using local variables, then python is happily
> decrementing their reference count as your 'constructor' goes
> out of scope and they get garbage collected...
> 
> The convention is to make images instance variables. If you are
> paranoid about seeing the variables, mangle their names:
> 
>     self.__secret_image = ....

Thank's very much for your answer.

But...

Of course that when I write 
        my_img = PhotoImage(file = 'my_image.gif' )

inside a function or method, the reference my_img gets discarded when the
function exits. I understand that. The problem is that when I use this
reference to define an option for a Label instance in
        Label(self, image = my_img, bg = 'yellow').pack()

it should (at least I expected so) generate another reference to the same
object. But surprinsingly it seems don't.

This is quite different from what happen when I do the same with a text instead
an image. The code

##########################################################
from Tkinter import *
#
class TextIsNice(Toplevel):
    def __init__(self, master):
        Toplevel.__init__(self, master = master)
        my_txt = 'Text is nice!'
        Label(self, text = txt, bg = 'yellow').pack()
#
if __name__ == '__main__':  TextIsNice(None).mainloop()
##########################################################

works just fine, as I expected from Python usual behavior. So again, what's
wrong with images?

Maybe this has some relation with something special about PhotoImage: In the
debuging procedure, when I understood the need of explicitly keep a reference
to the image generated by PhotoImage, I tried this (which I thougth, naif me,
to be the same as declaring the reference global):

##########################################################
from Tkinter import *
#
my_img = PhotoImage(file = 'my_image.gif') # <-- GLOBAL !!
#
class NotSoFunny(Toplevel):
    def __init__(self, master):
        Toplevel.__init__(self, master = master)
        Label(self, image = my_img, bg = 'yellow').pack()
#
if __name__ == '__main__':  NotSoFunny(None).mainloop()
##########################################################

On execution Python presented me this traceback:

Traceback (innermost last):
  File "<stdin>", line 4, in ?
  File "/usr/lib/python1.5/lib-tk/Tkinter.py", line 1874, in __init__
    apply(Image.__init__, (self, 'photo', name, cnf, master), kw)
  File "/usr/lib/python1.5/lib-tk/Tkinter.py", line 1825, in __init__
    raise RuntimeError, 'Too early to create image'
RuntimeError: Too early to create image

So PhotoImage itself seems to need "something more". The only thing I can
imagine is PhotoImage needing to have "something" defined in its environment,
and that this "something" is silently defined by *others* (which looks poor
style to me). So I tried

##########################################################
from Tkinter import *
#
dummy_call_to_perform_magic_under_the_wood = Tk()
#
my_img = PhotoImage(file = 'my_image.gif') # <-- GLOBAL !!
#
class NotSoFunny(Toplevel):
    def __init__(self, master):
        Toplevel.__init__(self, master = master)
        Label(self, image = my_img, bg = 'yellow').pack()
#
if __name__ == '__main__':  NotSoFunny(None).mainloop()
##########################################################

and it worked "fine" (as far as we can say "fine" about voodoo code like this).

So yet again, what's wrong with images?

Thanks again, 
Sebrosa