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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_contents(self):
 """Fetch the signature contents. This is the main reason this class exists, so we can compute this once and cache it regardless of how many target or source Nodes there are. """

        try:
            return self._memo['get_contents']
        except KeyError:
            pass
        env = self.get_build_env()

        action_list = self.get_action_list()
        all_targets = self.get_all_targets()
        all_sources = self.get_all_sources()

        result = bytearray("",'utf-8').join([action.get_contents(all_targets,
                                                                 all_sources,
                                                                 env)
                                             for action in action_list])

        self._memo['get_contents'] = result
        return result