When a tkinter.font.Font is created from another font, Font.__init__ expanded it into concrete options with Tcl's font actual. For a named font this resolves the configured size, so a size specified in pixels (a negative size) was silently converted to a size in points (gh-143990).

font configure returns the configured options and preserves such a size, but it only accepts a font name, not a font description. So the font is now expanded with font configure when it is a named font, falling back to font actual when it is a font description:

try:
    font = tk.splitlist(tk.call("font", "configure", font))
except tkinter.TclError:
    font = tk.splitlist(tk.call("font", "actual", font))

Trying font configure first delegates the "is this a named font?" decision to Tcl, which is robust even for font names containing spaces.

A font description (a tuple or a string) is still resolved via font actual, since there is no way to parse it into options otherwise; wrapping it with exists=True (gh-143990, #152025) remains the way to use it without loss of precision.

Font.copy() has always been equivalent to constructing a Font from the original font (both went through font actual), so it is updated to match and now preserves the size too.

This is the general form of #143992, which restored the size only for a size given in a tuple.

• Issue: Different pixel-specified font sizes in tkinter #143990