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Different pixel-specified font sizes in tkinter #143990
Description
Bug report
Bug description:
import tkinter as tk
import tkinter.font as tkfont
root = tk.Tk()
font_tuple = ("Calibri", -14)
font = tkfont.Font(root, font_tuple)
lb1 = tk.Label(root, text="Hello", font=font_tuple)
lb1.pack()
lb2 = tk.Label(root, text="Hello", font=font)
lb2.pack()
root.update()
print(lb1.winfo_width(), lb1.winfo_height())
print(lb2.winfo_width(), lb2.winfo_height())
root.mainloop()The font size differs between tuples and Font objects.
The documentation states it can be specified in pixels, but is this a bug?
CPython versions tested on:
3.14
Operating systems tested on:
Windows
Linked PRs
- gh-143990: Preserve negative pixel sizes in tkinter.font.Font #143992
- gh-143990: Allow tkinter.font.Font to wrap a font description #152025
- gh-143990: Preserve the size when creating a Font from a named font #153267
- gh-143990: Do not assume the requested font size in test_font #153322
- [3.15] gh-143990: Preserve the size when creating a Font from a named font (GH-153267) #153323
- [3.14] gh-143990: Preserve the size when creating a Font from a named font (GH-153267) (GH-153323) #153341
- [3.13] gh-143990: Preserve the size when creating a Font from a named font (GH-153267) (GH-153323) #153342
Activity
pythongh-143990: Preserve negative pixel sizes in tkinter.font.Font
pythongh-143990: Preserve negative pixel sizes in tkinter.font.Font
pythongh-143990: Preserve negative pixel sizes in tkinter.font.Font
serhiy-storchaka commentedon Jan 20, 2026
This is more complex issue. Font description can be not only a tuple, but also a string like "TkTextFont -21 bold". It can also be in other format, like "-adobe-avant garde gothic-book-o-normal--0-0-0-0-p-0-iso8859-1".
The problem is that some
fontsubcommants support font description, while others only font name. The Font class tries to provide object oriented interface for this, and by default creates a new font from a file description. Then the name of this font instead of the original font description is used infont actual,font measureandfont metrics. There is a loss of precision betweenfont actualandfont create.pythongh-143990: Add What's New entry for tkinter.font.Font wrapping
serhiy-storchaka commentedon Jun 23, 2026
#152025 allows to wrap a font description, not only a named font.
gh-143990: Allow tkinter.font.Font to wrap a font description (GH-152025
serhiy-storchaka commentedon Jul 7, 2026
Addressed by #152025 and #153267. There are two parts to this:
("Calibri", -14)or a string) is expanded via Tcl'sfont actual, which resolves a size in pixels to points. This is inherent — a description can't be parsed into options otherwise. To use a description without loss of precision, wrap it withexists=True(gh-143990: Allow tkinter.font.Font to wrap a font description #152025):Font(root, ("Calibri", -14), exists=True)renders identically to the raw tuple.Fontfrom a named font now copies its configured options viafont configure(gh-143990: Preserve the size when creating a Font from a named font #153267), preserving a size specified in pixels.So a
Fontbuilt from a bare description still reports the resolved size by design, withexists=Trueas the exact-preservation path.pythongh-143990: Preserve the size when creating a Font from a named …
Merge branch 'main' into pythongh-143990-font-configure
encukou commentedon Jul 8, 2026
The Alpine buildbot is broken, likely because of this change. See e.g. https://buildbot.python.org/#/builders/301/builds/15551
gh-143990: Preserve the size when creating a Font from a named font (G…
serhiy-storchaka commentedon Jul 8, 2026
encukou commentedon Jul 8, 2026
serhiy-storchaka commentedon Jul 8, 2026
Should be fixed by #153322.
gh-143990: Do not assume the requested font size in test_font (GH-153322
pythongh-143990: Fix the 3.15 backport of pythonGH-153267
pythongh-143990: Drop a redundant comment in the 3.15 backport
[3.15] gh-143990: Preserve the size when creating a Font from a named…
[3.13] gh-143990: Preserve the size when creating a Font from a named…
[3.14] gh-143990: Preserve the size when creating a Font from a named…