tkinter missing TkDefaultFont

Bug report

Bug description:

Encountering problems looking up TkDefaultFont with Python 3.14.7 on Windows 10(x64), possibly due to the upgrade to Tcl/Tk 9.0.4 that occurred in the 3.14.7 Windows release ref.

The example script below demonstrates the problem:

import tkinter as tk
from tkinter import ttk
import tkinter.font as tkfont

app = tk.Tk()
style = ttk.Style()
font_name = style.lookup("TButton", "font")
font = tkfont.nametofont(font_name)
print(f"{font_name} is {font}")
app.mainloop()

This fails with the following traceback:

Traceback (most recent call last):
  File "C:\Users\jason\Documents\atform\master\font.py", line 8, in <module>
    font = tkfont.nametofont(font_name)
  File "C:\Users\jason\AppData\Local\Programs\Python\Python314\Lib\tkinter\font.py", line 25, in nametofont
    return Font(name=name, exists=True, root=root)
  File "C:\Users\jason\AppData\Local\Programs\Python\Python314\Lib\tkinter\font.py", line 96, in __init__
    raise tkinter._tkinter.TclError(
        "named font %s does not already exist" % (self.name,))
_tkinter.TclError: named font TkDefaultFont does not already exist

This example runs normally on Python versions up to and including 3.14.6, but fails on 3.14.7.

CPython versions tested on:

3.14

Operating systems tested on:

Windows

Linked PRs

Since the failure is in nametofont, the last 2 lines are not needed. Verified in 3.14.7, 3.15.0rc2, and 3.16.0-.

IDLE still successfully finds TkDefaultFont in idlelib.help line 177:
normalfont = self.findfont(['TkDefaultFont', 'arial', 'helvetica'])
self is an instance of a Text subclass with this method:

    def findfont(self, names):
        "Return name of first font family derived from names."
        for name in names:
            if name.lower() in (x.lower() for x in tkfont.names(root=self)):
                font = tkfont.Font(name=name, exists=True, root=self)
                return font.actual()['family']
            elif name.lower() in (x.lower()
                                  for x in tkfont.families(root=self)):
                return name

I am pretty sure I did not write this.

@serhiy-storchaka

It turns out that this does seem to be a Tcl/Tk 9 change; style.lookup("TButton", "font") no longer returns a str, but a Tcl_Obj wrapping a Tk font object. The good news is that there's a simple workaround; call nametofont(str(font_name)).

It might be worth fixing nametofont to accept a Tcl_Obj whose typename is font (or otherwise just call str on name), but I think we need @serhiy-storchaka's opinion there.

Perhaps it may be better to apply the conversion to the return value of style.lookup() so other uses of that function continue to receive a string. Additionally, the name of the function nametofont() does somewhat imply conversion of a name(str) to a font, not a font to a font.

See also gh-153513, where Serhiy specifically left font objects as Tcl_Obj in the changes for that issue.

gh-156961: Fix tkinter.font.Font for a font name returned as a Tcl ob…

[3.13] gh-156961: Fix tkinter.font.Font for a font name returned as a…

[3.14] gh-156961: Fix tkinter.font.Font for a font name returned as a…

pythongh-156961: Fix tkinter.font.Font for a font name returned as a …

[3.15] gh-156961: Fix tkinter.font.Font for a font name returned as a…

Navigation Menu

Repository navigation

tkinter missing TkDefaultFont #156961

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

tkinter missing TkDefaultFont #156961

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

Activity

terryjreedy commented on Sep 5, 2026

zware commented on Sep 5, 2026

jvalenzuela commented on Sep 5, 2026

zware commented on Sep 5, 2026

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions