<Topic> Tkinter Treeview styling in the background process

Question

[Topic] Tkinter Treeview styling in the background process

Platform specification:

• Pop!_OS 22.04 LTS
• Python 3.10.12 (main, Nov 20 2023, 15:14:05) [GCC 11.4.0] on linux
• tk.TclVersion == tk.TkVersion == 8.6
• echo 'puts [info patchlevel];exit 0' | tclsh == 8.6.12

Hello Community,

I have created a Tk interface for a superordinate project that should function as an independent popup like those in the tk.filedialog module. Since this is to be completely deleted after the input query and this leads to

1. internal errors in Tk;
2. problems when calling the interface again

and the proposed solution of using tk.Toplevel did not produce the desired result, I decided to use a wrapper that executes the interface in an independent process in the background. The values are retrieved from the main process via a socket.

So after this issue was resolved, some other weird behavior occurred regarding the styling of ttk.treeview. With more trial-and-error than I would have liked, a satisfactory result was nevertheless achieved.

The Issue

Although the tk objects are all created in the same process, it seems to matter where the styling is defined.

<Main process>
|   <Popup process>
|   |   root = make() {
|   |       root = tk.Tk()
|   |       widget = Widget(root) {
|   |           ...
|   |           [3]
|   |       }
|   |       ...
|   |       [2]
|   |       return root
|   |   }
|   |   [1]
|   |   root.mainloop()
|
|<Popup process>.start()

The styling of ttk.Treeview is only fully applied when the styling code is defined/executed at position [2] and then (before the return) root.update_idletasks() is executed.

However, if the styling code is defined/executed at position [3] or root.update_idletasks() is only executed after the return at position [1], the parameter font=[('selected', font)] of

style = ttk.Style()

style.configure(
    "Treeview",
    weight="normal",
    size=10
)
__font = tkFont.Font()
__font.configure(underline=True, weight="bold", size=10)
style.map('Treeview', font=[('selected', __font)], background=[], foreground=[('selected', '#000000')])

is not applied.

(v1)

Update

Ok, the problem is probably that the object font only exists locally in the function context. So if font is saved in an existing object, e.g. by global font at the beginning of the function, the styling font=[('selected', font)] is also applied.

My guess

The problem seems to be related to the python-tk interface and the garbage collector.

So tk(-inter) uses the reference to the original object and does not create a copy or a separate object. For some reason, this reference is not recognized by the garbage collector and the local object is deleted after the function is finished. Tk then handles the error internally.

(v2)

Asked on Stackoverflow.

The entire code can be accessed on Github.