This method determines, for each string in the ukulele, the location of each fret in each string. When pressed and strummed individually, it will produce a sound from one of the notes in the ``notes`` parameter.

def get_fret_index(notes):
   frets = {}
   for i in range(len(notes)):
      frets[i] = {}
      for j in range(len(notes[i])):
         frets[i][j] = notes[i].index(notes[i][j])
   return frets