code: def set_iam_policy(self, policy):
          
          instance_admin_client = self._client.instance_admin_client
          resp = instance_admin_client.set_iam_policy(
              resource=self.name, policy=policy.to_pb()
          )
          return Policy.from_pb(resp)
docs: Sets the access control policy on an instance resource. Replaces any
          existing policy.
  
          For more information about policy, please see documentation of
          class `google.cloud.bigtable.policy.Policy`
  
          For example:
  
          .. literalinclude:: snippets.py
              :start-after: [START bigtable_set_iam_policy]
              :end-before: [END bigtable_set_iam_policy]
  
          :type policy: :class:`google.cloud.bigtable.policy.Policy`
          :param policy: A new IAM policy to replace the current IAM policy
                         of this instance
  
          :rtype: :class:`google.cloud.bigtable.policy.Policy`
          :returns: The current IAM policy of this instance.