On macOS with Python 3.15, test_idle and test_tkinter fail with _tkinter.TclError: invalid command name "::tk::unsupported::MacWindowStyle" on Tk/Tcl 9.1 #159517

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1. vstinner

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   testsTests in the Lib/test dirTests in the Lib/test dir

   OS-mac

   topic-tkinter

   on Oct 16, 2026
2. vstinner commented on Oct 16, 2026

   

   vstinner

   on Oct 16, 2026

   MemberAuthor

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   Example of failure:

   ERROR: test_open_and_close (idlelib.idle_test.test_searchbase.SearchDialogBaseTest.test_open_and_close)
   ----------------------------------------------------------------------
   Traceback (most recent call last):
     File "/Users/runner/work/cpython/cpython/Lib/idlelib/idle_test/test_searchbase.py", line 52, in test_open_and_close
       self.dialog.open(text)
       ~~~~~~~~~~~~~~~~^^^^^^
     File "/Users/runner/work/cpython/cpython/Lib/idlelib/searchbase.py", line 55, in open
       self.create_widgets()
       ~~~~~~~~~~~~~~~~~~~^^
     File "/Users/runner/work/cpython/cpython/Lib/idlelib/searchbase.py", line 103, in create_widgets
       _setup_dialog(top)
       ~~~~~~~~~~~~~^^^^^
     File "/Users/runner/work/cpython/cpython/Lib/tkinter/simpledialog.py", line 265, in _setup_dialog
       w.tk.call("::tk::unsupported::MacWindowStyle", "style",
       ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                 w, "moveableModal", "")
                 ^^^^^^^^^^^^^^^^^^^^^^^
   _tkinter.TclError: invalid command name "::tk::unsupported::MacWindowStyle"
   

   cc @terryjreedy @serhiy-storchaka
3. vstinner

   changed the title [-]test_idle and test_tkinter fail with `_tkinter.TclError: invalid command name "::tk::unsupported::MacWindowStyle"` on Tk 9.1/Tcl 9.1[/-] [+]On macOS, test_idle and test_tkinter fail with `_tkinter.TclError: invalid command name "::tk::unsupported::MacWindowStyle"` on Tk/Tcl 9.1[/+] on Oct 16, 2026
4. vstinner

   changed the title [-]On macOS, test_idle and test_tkinter fail with `_tkinter.TclError: invalid command name "::tk::unsupported::MacWindowStyle"` on Tk/Tcl 9.1[/-] [+]On macOS with Python 3.15, test_idle and test_tkinter fail with `_tkinter.TclError: invalid command name "::tk::unsupported::MacWindowStyle"` on Tk/Tcl 9.1[/+] on Oct 16, 2026
5. vstinner

   added 3 commits that reference this issue on Oct 16, 2026

   pythongh-159517: Modernize tkinter.simpledialog

   ...

   b25326b

   [3.15] gh-159517: Modernize tkinter.simpledialog (#159518)

   ...

   173dabe

   [3.14] gh-159517: Modernize tkinter.simpledialog (GH-159518) (#159522)

   ...

   8c27786
6. serhiy-storchaka commented on Oct 16, 2026

   

   serhiy-storchaka

   on Oct 16, 2026

   Member

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   Thank you, @vstinner. I did not expect CI will use Tcl 9.1/Tk 9.1 so soon, especially on non-main branches. I do not recommend to use 9.1.0. It has many bugs in new features. The next bugfix release will came with their fixes, and also with many fixes of old bugs and important macOS fixes.

   #159527 fixes other use of ::tk::unsupported::MacWindowStyle in IDLE.
7. vstinner commented on Oct 16, 2026

   

   vstinner

   on Oct 16, 2026

   MemberAuthor

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   Thank you, @vstinner.

   You're welcome.

   I did not expect CI will use Tcl 9.1/Tk 9.1 so soon, especially on non-main branches. I do not recommend to use 9.1.0. It has many bugs in new features. The next bugfix release will came with their fixes, and also with many fixes of old bugs and important macOS fixes.

   The failed 3.15 job uses macOS 26 arm image. The surprising thing is that https://github.com/actions/runner-images/blob/main/images/macos/macos-26-arm64-Readme.md still mentions "Tcl/Tk 8.6.18" whereas it was "Tcl/Tk 9.0" a few hours ago, and it's now "Tcl/Tk 9.1". The README is outdated, and I looked at the wrong README :-)