code: def set_icon_file(self, filename, rel="icon"):
          
          mimetype, encoding = mimetypes.guess_type(filename)
          self.add_child("favicon", '<link rel="%s" href="%s" type="%s" />'%(rel, filename, mimetype))
docs: Allows to define an icon for the App
  
              Args:
                  filename (str): the resource file name (ie. "/res:myicon.png")
                  rel (str): leave it unchanged (standard "icon")