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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 viewers(self):
 """Legacy access to viewer role. DEPRECATED: use ``policy["roles/viewers"]`` instead """

        result = set()
        for role in self._VIEWER_ROLES:
            for member in self._bindings.get(role, ()):
                result.add(member)
        return frozenset(result)