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Hello. In order to group several instances of a given application under one icon in the desktop launcher (I am using Ubuntu 17.04) they must have the same appName property of the WM_CLASS string. For example, if I run emacs twice:
$ emacs &
$ emacs &
Both instances will show up under the Emacs icon in the desktop launchbar. The reason is that both instances have the same WM_CLASS string. We can check this string using
$ xprop WM_CLASS
and then click on the Emacs window. It then shows:
WM_CLASS(STRING) = "emacs", "Emacs"
Here "emacs" is the resource (appName), and "Emacs" is the className.
Now, consider this program (my-tkapp.py):
#! /usr/bin/env python
import tkinter as tk
root = tk.Tk(className='myTkApp')
label = tk.Label(root, text="Hello World")
label.pack()
root.mainloop()
If I run this program twice:
$ my-tkapp.py &
$ my-tkapp.py &
and then run xprop to check the WM_CLASS property of both windows, the first window gives:
WM_CLASS(STRING) = "myTkApp", "Mytkapp"
whereas the second gives:
WM_CLASS(STRING) = "myTkApp #2", "Mytkapp"
Note that tkinter has added a #2 suffix to the app name property. This is not desired. It makes the window manager group the two windows under separate icons in the desktop launch bar.
How can I keep the same appName property of the WM_CLASS string for different instances of my application?
Note: This question was first asked at stackoverflow.com:
https://stackoverflow.com/q/44795622/2173773
I tried to follow the source from the call:
root = tkinter.Tk(className='myTkApp')
but at 5 levels down on the stack I ended up inside TCL code, and I was not able to determine who was responsible for adding the "#2" suffix.
However, a similar perl script gives the same behavior, so I suspect the problem is within the TCL TK code. Is there a way to change the
WM_CLASS property of the window after the call to tkinter.Tk, but before entering mainloop() in order to work around the issue?
After entering the mainloop(), I guess it is too late to do anything, since then the icon is already displayed in the window manager's launch bar.
I am using Ubuntu 17.04 and Python version 3.6.1.
Best regards,
Håkon Hægland

> tkinter has added a #2
I think you yourself proved otherwise. Additional evidence is that ' #2' is not added on Windows. I have 3 windows titled 'myApp' stacked behind my installed python/IDLE icon. root.winfo_class() returns the class name capitalized, but the window title is not. root.winfo_class('newname') does not work. Note: I added more chars to the label to make it big enough to force the window to be big enough to display the title.
There might be a reason why tcl deduplicates class names on *nix. So even if you found a way to set a classname after the Tk call, tcl might still deduplicate it. Or we might decide not to force change the current behavior.
I suspect that this will be closed as a 3rd-party issue.

I concur with Terry. This is not a Tkinter issue, this is a Tk issue.
Ask help on Tcl/Tk resources. If this is considered a bug open a ticket on the Tk tracker: https://core.tcl.tk/tk/tktnew .