Tkinter `ttk.Treeview` `.selection()` gives incorrect result, when `crtl`+`left-click` deselecting the last selected item

[ZelphirKaltstahl]

Bug report

Bug description:

My environment is the following:

• I am using Python 3.13.5
• on Debian GNU/Linux 13 (trixie)
• (desktop environment: KDE)
• tk.TkVersion: 8.6
• ttk.tkinter.TkVersion: 8.6
• tk system package:

  $ apt-cache policy tk
  tk:
    Installed: (none)
    Candidate: 8.6.16
    Version table:
       8.6.16 500
          500 http://deb.debian.org/debian trixie/main amd64 Packages
  

• apt list --installed | grep tk:

  ...
  python3.13-tk/stable,now 3.13.5-2 amd64 [installed,automatic]
  ...
  

What I have observed is, that there seems to be a bug in the method treeview.selection(). Steps to reproduce:

1. register handlers for "<<TraverseIn>>", something along the lines of:

    def __init__(self ...):
        self.treeview.bind(
            "<<TraverseIn>>",
            self._on_traverse_out_treeview
        )
    ...
    def _on_traverse_out_treeview(self, event: tk.Event) -> str | None:
        logger.info(self.treeview.selection())

2. start the application
3. select one item in the treeview using mouse left click
4. deselect the only one selected item in the treeview, using ctrl + left click
5. tab through the widgets, until you focus the treeview again
6. observe how tkinter still logs the deselected item as selected

Workaround

I have found a workaround, which I am currently using.

        # Binding for working around treeview selection bug.
        self.treeview.bind(
            EventName.TRAVERSE_OUT.value,
            self._on_traverse_out_treeview
        )
    ...
    def _on_traverse_out_treeview(self, event: tk.Event) -> None:
        if len(self.treeview.selection()) == 0:
            self.treeview.selection_clear()
            self.treeview.focus("")

This forces the selection and focus to clear, if no item is selected when tabbing out. Then, when tabbing and reaching the treeview again, if there is no visually selected item, the selection state will have been cleared and .selection() will give the correct result.

Side-effects

• Not yet observed. I only found this workaround today.

CPython versions tested on:

3.13

Operating systems tested on:

Linux

[picnixz]

cc @serhiy-storchaka @terryjreedy

[serhiy-storchaka]

Tkinter is mostly a thin wrapper around Tcl/Tk. In that case it is exactly a thin wrapper:

    def selection(self):
        """Returns the tuple of selected items."""
        return self.tk.splitlist(self.tk.call(self._w, "selection"))

If the behavior looks incorrect to you, please report a bug on the Tk bug tracker.

[ZelphirKaltstahl]

Reported here: https://core.tcl-lang.org/tk/tktview/047b2297a74b1d282835094b3b293e9e374de730.