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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def __updateNavButtons(self):
 """ Updates the navigation buttons that might be on the device screen. """


        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