code: def split_key_string(key):
      
      key, mode = key.split()
      return KEY_TO_SEMITONE[key.lower()], mode
docs: Splits a key string (of the form, e.g. ``'C# major'``), into a tuple of
      ``(key, mode)`` where ``key`` is is an integer representing the semitone
      distance from C.
  
      Parameters
      ----------
      key : str
          String representing a key.
  
      Returns
      -------
      key : int
          Number of semitones above C.
      mode : str
          String representing the mode.