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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_sig(self):
 """ A helper method for get_cachedir_bsig. It computes and returns the signature for this node's contents. """


        try:
            return self.contentsig
        except AttributeError:
            pass

        executor = self.get_executor()

        result = self.contentsig = SCons.Util.MD5signature(executor.get_contents())
        return result