How to check if font do support characters (codepoints?)

[buhtz]

I would like to know if the currently selected font do support a specific character (or string) or if it just renders it with the rectangle-characters like this □□□□□.

Can I check this somehow on the fly while my PyQt5 application is running?

label = QLabel('string to check')
label.rendered?

Or "asking" the font:
label.font.codepoints_available('string to check')

[KH-219Design]

Caveats: On a day-to-day basis I work in C++ and rarely in python. Furthermore, I have not attempted any of what I am sharing here.

However, it seems that using the lower-level C libraries like libfreetype and/or harfbuzz, this is possible. So it seems likely to me that someone has created a python wrapper of some kind that would expose it in python.

Apparently (in C), the libfreetype function FT_Get_Char_Index will return 0 if the desired glyph does not exist in a given font:

http://refspecs.linux-foundation.org/freetype/freetype-doc-2.1.10/docs/reference/ft2-base_interface.html#FT_Get_Char_Index

And here is an example of someone using pyharfbuzz in a similar way:

https://askubuntu.com/a/1186237/231504