code: def _block_format_index(index):
      """
      Convert a list of indices ``[0, 1, 2]`` into ``"arrays[0][1][2]"``.
      """
      idx_str = "".join(
          "[{}]".format(i) for i in index if i is not None
      )
      return "arrays" + idx_str
  
file_path: mars/mars/tensor/merge/block.py
imports: import functools
  import itertools
  import operator
  import numpy
  from ..datasource.empty import empty
  from ..datasource.array import array
label_desc: Use image node_id 1 for calling a global function with example usage: _block_format_index(index) and returns: unknown