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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 _create_mappings(self, spec):
 """ Create property name map based on aliases. """

        ret = dict(zip(set(spec.fields), set(spec.fields)))
        ret.update(dict([(n, s.alias) for n, s in spec.fields.items() if s.alias]))
        return ret