code: def h2o_H2OFrame_substring():
      """
      Python API test: h2o.frame.H2OFrame.substring(start_index, end_index=None)
  
      Copied from pyunit_sub_gsub.py
      """
      frame = h2o.import_file(
          path=pyunit_utils.locate("smalldata/iris/iris.csv")
      )
      frame["C5"] = frame["C5"].substring(0, 5)
  
      assert (
          frame["C5"] == "Iris-"
      ).sum() == frame.nrow, (
          "h2o.H2OFrame.substring() command is not working."
      )
  
label_desc: Use image node_id 1 for calling a global function with example usage: h2o_H2OFrame_substring() without return types