title: Read GTK Radio Button signal only when selected
body: <p>GTK's "toggled" signal fires when a radio button is selected, but before that, it also fires upon deselection of the previously selected radio button.</p>
  
  <p>I am working with a GUI that uses radio buttons, each representing a group of entities. The first of the pair of "toggled" signals is triggering some unwanted updates to other fields in the GUI -- updates that I only want to happen when the newly selected button triggers the callback. How do I work around this signal and limit the callback function to only operate on selection instead of deselection? I've considered a flag variable within the class I'm coding, but perhaps there is a more GTK-approved technique.</p>