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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, value):
 """Update viewers. DEPRECATED: use ``policy["roles/viewers"] = value`` instead. """

        warnings.warn(
            _ASSIGNMENT_DEPRECATED_MSG.format("viewers", VIEWER_ROLE),
            DeprecationWarning,
        )
        self[VIEWER_ROLE] = value