code: def tab_navigate(self, delta=1):
          
          if delta > 0 and self.currentIndex() == self.count()-1:
              index = delta-1
          elif delta < 0 and self.currentIndex() == 0:
              index = self.count()+delta
          else:
              index = self.currentIndex()+delta
          self.setCurrentIndex(index)
docs: Ctrl+Tab