<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_iam_policy(self, policy):
 """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. """

        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)