code: def identify(s):
      
      if is_pinyin(s):
          return PINYIN
      elif is_zhuyin(s):
          return ZHUYIN
      elif is_ipa(s):
          return IPA
      else:
          return UNKNOWN
docs: Identify a given string's transcription system.
  
      *s* is the string to identify. The string is checked to see if its
      contents are valid Pinyin, Zhuyin, or IPA. The :data:`PINYIN`,
      :data:`ZHUYIN`, and :data:`IPA` constants are returned to indicate the
      string's identity.
      If *s* is not a valid transcription system, then :data:`UNKNOWN` is
      returned.
  
      When checking for valid Pinyin or Zhuyin, testing is done on a syllable
      level, not a character level. For example, just because a string is
      composed of characters used in Pinyin, doesn't mean that it will identify
      as Pinyin; it must actually consist of valid Pinyin syllables. The same
      applies for Zhuyin.
  
      When checking for IPA, testing is only done on a character level. In other
      words, a string just needs to consist of Chinese IPA characters in order
      to identify as IPA.