Lists the instances.

        Instances are returned in lexicographical order.

        :rtype: ~collections.Iterable[.Instance]

def list_instances(self):
        """
        Lists the instances.

        Instances are returned in lexicographical order.

        :rtype: ~collections.Iterable[.Instance]
        """
        # Server does not do pagination on listings of this resource.
        # Return an iterator anyway for similarity with other API methods
        response = self.get_proto(path='/instances')
        message = rest_pb2.ListInstancesResponse()
        message.ParseFromString(response.content)
        instances = getattr(message, 'instance')
        return iter([Instance(instance) for instance in instances])