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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 _get_controller_help(self, controller):
 """Return the value of the HELP attribute for a controller that should describe the functionality of the controller. :rtype: str|None """

        if hasattr(self._controllers[controller], 'HELP'):
            return self._controllers[controller].HELP
        return None