code: def __updateNavButtons(self):
          
  
          navButtons = None
          for v in self.views:
              if v.getId() == 'com.android.systemui:id/nav_buttons':
                  navButtons = v
                  break
          if navButtons:
              self.navBack = self.findViewById('com.android.systemui:id/back', navButtons)
              self.navHome = self.findViewById('com.android.systemui:id/home', navButtons)
              self.navRecentApps = self.findViewById('com.android.systemui:id/recent_apps', navButtons)
          else:
              if self.uiAutomatorHelper:
                  print >> sys.stderr, "WARNING: nav buttons not found. Perhaps the device has hardware buttons."
              self.navBack = None
              self.navHome = None
              self.navRecentApps = None
docs: Updates the navigation buttons that might be on the device screen.