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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 """ Abbreviate a string, adding an indicator like an ellipsis if required. """

  if not string or not max_len or len(string) <= max_len:
    return string
  elif max_len <= len(indicator):
    return string[0:max_len]
  else:
    return string[0:max_len - len(indicator)] + indicator