code: def _iter(self):
      chunk_graph = self._cur_chunk_graph
  
      to_update_tileables = []
      visited = set()
  
      if chunk_graph is not None:
          # last tiled chunks, add them to processed
          # so that fetch chunk can be generated.
          # Use chunk key as the key to make sure the copied chunk can be build to a fetch.
          processed_chunks = (
              c.chunk.key if isinstance(c, FUSE_CHUNK_TYPE) else c.key
              for c in chunk_graph.result_chunks
          )
          self._processed_chunks.update(processed_chunks)
  
      result_chunks = []
      chunk_graph = self._cur_chunk_graph = ChunkGraph(result_chunks)
  
      next_tileable_handlers = []
      # tile
      for tile_handler in self._gen_tileable_handlers(
          next_tileable_handlers
      ):
          self._tile(
              chunk_graph,
              tile_handler.tileable,
              tile_handler.handler,
              next_tileable_handlers,
              to_update_tileables,
              visited,
          )
      self._tileable_handlers = next_tileable_handlers
      # gen result chunks
      self._gen_result_chunks(chunk_graph, next_tileable_handlers)
      # prune unused chunks
      prune_chunk_graph(chunk_graph)
  
      self._curr_iter += 1
  
      return to_update_tileables
  
imports: import dataclasses
  import functools
  from typing import Callable, Dict, Generator, Iterable, List, Optional, Set, Type, Union
  from ....core import FUSE_CHUNK_TYPE, CHUNK_TYPE, TILEABLE_TYPE
  from ....typing import EntityType, TileableType, ChunkType
  from ....utils import copy_tileables, build_fetch
  from ...entity.tileables import handler
  from ...mode import enter_mode
  from ..entity import TileableGraph, ChunkGraph
  from .base import AbstractGraphBuilder
label_desc: Use image node_id 8 for calling the Tiler obj's underlying member method code with example usage: obj._iter() and returns: to_update_tileables