problem with Font changing

[momesana]

If you intend to change font in whole ui (not concrete widgets) u may use styleSheet.
The simplest way to use a styleSheet is to open ui in qtdesigner, and paste something like

It is possible to apply a Stylesheet to a single widget, or to a class of widgets, or to widgets with some certain properties:

// applies to the QLabel object with the objectName "certain-label"
QLabel#certain-label {
    color: blue;
   font-weight: bold;
}

// applies to the QLabel object with the objectName "certain-label"
QLabel#certain-label {
    color: blue;
   font-weight: bold;
}

To copy to clipboard, switch view to plain text mode 

He could also call setStyleSheet on the widget to force a certain stylesheet for the widget after applying the other stylesheet on the application.

Stylesheets can much more than this ...