class_docstr: Convert between text-label and text-index 
class_docstr_tok: ["Convert","between","text-label","and","text-index"]
code: def add_special_char(self, dict_character):
      return dict_character
  
imports: import cv2
  import copy
  import numpy
  import math
  import re
  import sys
  import argparse
  import string
  from copy import deepcopy
label_desc: Use image node_id 2 for calling the BaseRecLabelDecode obj's underlying member method code with example usage: obj.add_special_char(dict_character) and returns: dict_character