code: def __init__(self):
      # For faster import mars.
      if SubtaskFusion.type_DataFrameConcat is None:
          from ....dataframe.merge.concat import DataFrameConcat
  
          SubtaskFusion.type_DataFrameConcat = DataFrameConcat
      self._typed_chunks = defaultdict(list)
  
imports: import itertools
  import logging
  from collections import deque, defaultdict
  from typing import Dict, List, Tuple, Type, Union
  from ....config import Config
  from ....core import ChunkGraph, ChunkType, enter_mode, DAG
  from ....core.operand import Fetch, VirtualOperand, LogicKeyGenerator, MapReduceOperand, OperandStage, ShuffleProxy, ShuffleFetchType
  from ....lib.ordered_set import OrderedSet
  from ....resource import Resource
  from ....typing import BandType, OperandType
  from ....utils import build_fetch, build_fetch_shuffle, tokenize
  from ...subtask import SubtaskGraph, Subtask
  from ..core import Task, new_task_id, MapReduceInfo
  from .assigner import AbstractGraphAssigner, GraphAssigner
  from .fusion import Coloring
label_desc: Use image node_id 1 to create a new SubtaskFusion object  with example: obj = SubtaskFusion()