Different pixel-specified font sizes in tkinter

[Kawasaki5963]

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

[serhiy-storchaka]

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 font subcommants 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 in font actual, font measure and font metrics. There is a loss of precision between font actual and font create.