Terry Reedy at 2016/3/2 UTC+8 3:04:10PM wrote：
> On 3/1/2016 9:35 PM, [email protected] wrote:
> > Recently I was puzzled by a tkinter problem. The codes below (from a book)
> > can display the picture correctly.
> >
> > gifdir = "../gifs/"
> > from tkinter import *
> > win = Tk()
> > photo = PhotoImage(file=gifdir + "ora-pp.gif")
> > Button(win, image=photo).pack()
> > win.mainloop()
>
> Since photo is a global name, the binding remain until you explicitly
> delete it or exit the app.
>
> > And the codes below (from another book) will also work.
> >
> > class DrumMachine:
> > ....
> > ....
> > def create_play_bar(self):
> > ....
> > ....
> > photo = PhotoImage(file='images/signature.gif')
> > label = Label(playbar_frame, image=photo)
> > label.image = photo
> > label.grid(row=start_row, column=50, padx=1, sticky='w')
> > ....
> > ....
>
> Here photo is a local name and the binding disappears when the function
> exits. I would rewrite it to follow pattern 1.
>
> self.photo = PhotoImage(file='images/signature.gif')
> label = Label(playbar_frame, image=self.photo)
>
> To me, saving an attribute reference is not worth the extra line.
>
> > In the second example, I noticed that the "photo" was referenced two times
> > and I think it might be a redundancy so I remove the line "label.image =
> > photo". But it fails then.
>
> On another question, I made the same suggestion. Oops.
>
> --
> Terry Jan Reedy
Thanks, Terry. After reading your reply I noticed that I had make a mistake.
The "image" is not an attribute of the Button. It's an option. The
"label.image=photo" does a different thing. But it didn't help on solving my
puzzle.
If the problem was caused by the "photo" is a local, then binding the "photo"
to an local attribute ("label" is a local too) seems no meaning at all. But it
did make difference! No idea how the underneath mechanism works.
I run this example under the pdb and it can display the picture correctly even
without the "label.image=photo" statement. Why it fails on running at real
time? tk event scheduling? I don't know.
--Jach
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