class_docstr: A helper class that represents input string that to be modified.
  for example:
      1. CnTextField(['今天', '天气', '不错'],None)
      2. CnTextField('今天天气不错',None)
  
  :param str or list field_value: the value of the field.
  :param int mask: mask label.
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docstr: Delete words at indices and remove their mask value.
  
  :param [int|list|slice] indices:
      each index can be int indicate replace single item
          or their list like [1, 2, 3].
      each index can be list like (0,3) indicate replace items
          from 0 to 3(not included) or their list like [(0, 3), (5,6)]
      each index can be slice which would be convert to list.
  :return: Modified TextField object.
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code: def delete_at_indices(self, indices):
      r"""
      Delete words at indices and remove their mask value.
  
      :param [int|list|slice] indices:
          each index can be int indicate replace single item
              or their list like [1, 2, 3].
          each index can be list like (0,3) indicate replace items
              from 0 to 3(not included) or their list like [(0, 3), (5,6)]
          each index can be slice which would be convert to list.
      :return: Modified TextField object.
  
      """
      mask_value = delete_at_scopes(self.mask, indices)
      field_value = delete_at_scopes(self.tokens, indices)
  
      return self.new_field(field_value, mask=mask_value)
  
imports: from .field import Field
  from ....common.utils.list_op import *
  from ....common.preprocess.cn_processor import CnProcessor
  from ....common.settings import ORIGIN, TASK_MASK, MODIFIED_MASK
label_desc: Use image node_id 21 for calling the CnTextField obj's underlying member method code with example usage: obj.delete_at_indices(indices) and returns: self