code: def replace_symbol_to_no_symbol(pinyin):
      
      def _replace(match):
          symbol = match.group(0)  # 带声调的字符
          # 去掉声调: a1 -> a
          return RE_NUMBER.sub(r'', PHONETIC_SYMBOL_DICT[symbol])
  
      # 替换拼音中的带声调字符
      return RE_PHONETIC_SYMBOL.sub(_replace, pinyin)
docs: 把带声调字符替换为没有声调的字符