code: def instance(
          self,
          instance_id,
          configuration_name=None,
          display_name=None,
          node_count=DEFAULT_NODE_COUNT,
      ):
          
          return Instance(instance_id, self, configuration_name, node_count, display_name)
docs: Factory to create a instance associated with this client.
  
          :type instance_id: str
          :param instance_id: The ID of the instance.
  
          :type configuration_name: string
          :param configuration_name:
             (Optional) Name of the instance configuration used to set up the
             instance's cluster, in the form:
             ``projects/<project>/instanceConfigs/<config>``.
             **Required** for instances which do not yet exist.
  
          :type display_name: str
          :param display_name: (Optional) The display name for the instance in
                               the Cloud Console UI. (Must be between 4 and 30
                               characters.) If this value is not set in the
                               constructor, will fall back to the instance ID.
  
          :type node_count: int
          :param node_count: (Optional) The number of nodes in the instance's
                              cluster; used to set up the instance's cluster.
  
          :rtype: :class:`~google.cloud.spanner_v1.instance.Instance`
          :returns: an instance owned by this client.