class_docstr: Transformation controller which applies multi transformations
  to each data sample.
class_docstr_tok: ["Transformation","controller","which","applies","multi","transformations","to","each","data","sample","."]
docstr: Check whether fields is legal.
docstr_tok: ["Check","whether","fields","is","legal","."]
code: def _check_fields(self):
      """
      Check whether fields is legal.
  
      """
      if isinstance(self.fields[0], str):
          pass
      elif isinstance(self.fields, list):
          if len(self.fields) == 1 and isinstance(self.fields[0], str):
              self.fields = self.fields[0]
          else:
              raise ValueError(
                  "Task {0} not support transform multi fields: {0}".format(
                      self.task, self.fields
                  )
              )
      else:
          raise ValueError(
              "Task {0} not support input fields type: {0}".format(
                  self.task, type(self.fields)
              )
          )
  
imports: from tqdm import tqdm
  from abc import ABC
  from itertools import product
  from ...input.dataset import Dataset
  from ...common.utils.seed import set_seed
  from ...common.utils.logger import logger
  from ...common.preprocess import EnProcessor
  from ...common.utils.load import pkg_class_load, load_module_from_file
  from ..transformation import Transformation, Pipeline
  from ..subpopulation import SubPopulation
  from ...common.settings import TASK_TRANSFORMATION_PATH, ALLOWED_TRANSFORMATIONS, TASK_SUBPOPULATION_PATH, ALLOWED_SUBPOPULATIONS
label_desc: Use image node_id 10 for calling the Generator obj's underlying member method code with example usage: obj._check_fields() without return types