gh-143990: Preserve negative pixel sizes in tkinter.font.Font

[dawdameet]

gh-143990: Preserve negative pixel sizes in tkinter.font.Font

Summary

This PR fixes a bug where tkinter.font.Font objects would lose their negative sign (representing pixel size) and convert it to a positive integer (representing points) during initialization.

details

The Font.init method calls tk.call("font", "actual", font). In Tcl/Tk, font actual resolves the requested font to the system's closest match. If a font is requested in pixels (e.g., -14), Tcl calculates the equivalent point size (e.g., 11) based on the current DPI.

The current implementation in tkinter/font.py was blindly accepting this resolved value and overwriting the user's original request. This fix checks if the input was a tuple containing a size, and if so, restores that specific size after the font actual call.

Changes

Modified Lib/tkinter/font.py to preserve the user-requested size.
Added a regression test test_negative_pixel_size to Lib/test/test_tkinter/test_font.py.
Verified that Font.cget("size") now returns the correct negative integer.

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[Kawasaki5963]

Thank you.

I wasn't sure where to comment this, but I found a case where the error wasn't fixed.

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()

font = tkfont.Font(root, lb1["font"]) #

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()