Why does my Tkinter GIF image disappear when inside a class?

Greg Krohn greg.invalid at capra.us.invalid
Wed Mar 3 08:33:46 CET 2004


midtoad wrote:
> I'm trying to display a GIF image in a label as the central area to a
> Tkinter GUI.   The image does not appear, though a space is made for it. 
> Why is this so?
> 
> I notice that I can display a GIF image in the central area of a simple
> menu-bar app as shown below in the first code sample. But, when I set up my
> app with a class, as shown below in the second code sample, the image
> disappears.   
> 
> How can I correct this? I'm sure the answer would jump out at me if I
> thought more clearly about it...
> 
> thanks
> S
> 
> ---
> #basicmenu.py : displays GIF image
> 
> 
> from Tkinter import *
> 
> 
> def callback(text):
>     print "called the callback!: "+text
> 
> root = Tk()
> 
> # create a menu
> menu = Menu(root)
> root.config(menu=menu)
> 
> filemenu = Menu(menu)
> menu.add_cascade(label="File", menu=filemenu)
> filemenu.add_command(label="New", command=callback('new'))
> filemenu.add_command(label="Open...", command=callback('open'))
> filemenu.add_separator()
> filemenu.add_command(label="Exit", command=callback('exit'))
> 
> helpmenu = Menu(menu)
> menu.add_cascade(label="Help", menu=helpmenu)
> helpmenu.add_command(label="About...", command=callback('about'))
> 
> img00 = PhotoImage(format='gif',data=
>              'R0lGODlhKwAQAJEAACWgA/3bYYNOGgAAACwAAAAAKwAQAAACfIyPqcsrD2M0'
>             +'oAJqa8h29yAkITiG3HWmKWiUrdtpseZdtcfmJSyjvf2Z5Q671u0wA9I+RtLj'
>             +'ZcwgfxglTTchjqS34JUrCUMQySOzih07Tb62eeneqSfU8vsmf65xZa8S/zI3'
>             +'dlLD5deRl1dlxdT4MYIA2TBJuSZ2iZkZVgAAOw==')
> 
> newLabel = Label(root,image=img00)
> t = str(img00.width()) + ' wide x ' + str(img00.height()) + ' high'
> newLabel.pack()
> Label(root,text='The image is\n'+t).pack()
> 
> mainloop()
> ---
> #basicmenu2gifobj.py : doesn't display image
> 
> from Tkinter import *
> 
> class gifMenu:
>     def __init__(self, parent):
> 
>         # create a menu
>         menu = Menu(parent)
>         parent.config(menu=menu)
> 
>         filemenu = Menu(menu)
>         menu.add_cascade(label="File", menu=filemenu)
>         filemenu.add_command(label="New", command=callback('new'))
>         filemenu.add_command(label="Open...", command=callback('open'))
>         filemenu.add_separator()
>         filemenu.add_command(label="Exit", command=callback('exit'))
> 
>         helpmenu = Menu(menu)
>         menu.add_cascade(label="Help", menu=helpmenu)
>         helpmenu.add_command(label="About...", command=callback('about'))
> 
>         img00 = PhotoImage(format='gif',data=
>               'R0lGODlhKwAQAJEAACWgA/3bYYNOGgAAACwAAAAAKwAQAAACfIyPqcsrD2M0'
>             +'oAJqa8h29yAkITiG3HWmKWiUrdtpseZdtcfmJSyjvf2Z5Q671u0wA9I+RtLj'
>             +'ZcwgfxglTTchjqS34JUrCUMQySOzih07Tb62eeneqSfU8vsmf65xZa8S/zI3'
>             +'dlLD5deRl1dlxdT4MYIA2TBJuSZ2iZkZVgAAOw==')
> 
>         newLabel = Label(parent,image=img00)
>         t = str(img00.width()) + ' wide x ' + str(img00.height()) + ' high'
>         newLabel.pack()
>         Label(parent,text='The image is\n'+t).pack()
> 
> class callback:
>     def __init__(self, text):
>         self.text = text
>     def __call__(self):
>         print 'Command is: ',self.text
> 
> ######################################################################
> 
> # Create GUI in root window for testing.
> if __name__ == '__main__':
>     title='Menu test with GIF'
>     root = Tk()
>     #Pmw.initialise(root)
>     root.title(title)
> 
>     #exitButton = Tkinter.Button(root, text = 'Exit', command =
> root.destroy)
>     #exitButton.pack(side = 'bottom')
>     gifMenu = gifMenu(root)
> 
> 
>     root.mainloop()

Short answer:
Replace img00 with self.img00

Longer answer:
It's a wart (as far as I'm concerned) in Tkinter. As soon as code 
execution falls out of __init__ (where img00 was created), the variable 
img00 is destroyed, hence Tkinter can't find the image. So you need to 
find some way of keeping the image persistant. Like making it an 
instance variable, like above, or making it global, etc.

greg



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