tl;dr: sometimes the UI can be written in a different language. Qt used to have an XML markup language that auto generated C++ UI code. Later, QML was introdu

tl;dr: sometimes the UI can be written in a different language. Qt used to have an XML markup language that auto generated C++ UI code. Later, QML was introduced - which is a JavaScript based UI runtime. There are Qt bindings for other languages, for example Python. So you could write business logic in Python and UI in QML.