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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 identifier(self):
 """Return a unique identifier for the given data set"""

        if self.background_identifier is None:
            idsum = self._identifier_data()
        else:
            idsum = hash_obj([self._identifier_data(),
                              self.background_identifier])
        return idsum