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Groups > comp.lang.python > #103843
| From | Terry Reedy <tjreedy@udel.edu> |
|---|---|
| Newsgroups | comp.lang.python |
| Subject | Re: How to know if an object is still be referenced? |
| Date | 2016-03-02 02:03 -0500 |
| Message-ID | <mailman.95.1456902233.20602.python-list@python.org> (permalink) |
| References | <8e9f1a84-cced-435e-a379-e1e2ac03f483@googlegroups.com> |
On 3/1/2016 9:35 PM, jfong@ms4.hinet.net 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
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How to know if an object is still be referenced? jfong@ms4.hinet.net - 2016-03-01 18:35 -0800
Re: How to know if an object is still be referenced? Terry Reedy <tjreedy@udel.edu> - 2016-03-02 02:03 -0500
Re: How to know if an object is still be referenced? jfong@ms4.hinet.net - 2016-03-02 03:35 -0800
Re: How to know if an object is still be referenced? sohcahtoa82@gmail.com - 2016-03-02 15:38 -0800
Re: How to know if an object is still be referenced? jfong@ms4.hinet.net - 2016-03-02 18:36 -0800
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