Now that we have had a glimpse of working with JSON files, this should be easy. Let's take a look at the first few lines of the chords.json file from the json directory:

{
 "Major" : [0, 4, 7],
 "Minor" : [0, 3, 7],
 "Sus4" : [0, 5, 7],
 "5" : [0, 4, 6],
 "Diminished" : [0, 3, 6],
 ...
}

This is very similar to the scales structure. Let's say we want to figure out what the C# major chord would look like. So we start with the C# key, which is 0. Then we look at the list of major chords, which read: [0, 4, 7]. So starting at C# the next key to highlight is 4 semitones above and the next is 7 semitones above C#. So the final chord structure for the C# major chord would be:

C#,    (C# + 4 semitones) ,      (C# + 7 semitones) 

The GUI is also very similar to the scales section:

We begin by adding a constant for the path to the chords.json file in  7.05 constants.py:

CHORDS_JSON_FILE = '../json/chords.json'

Next, we read the contents of this file in a new class attribute, self.chords:

 with open(CHORDS_JSON_FILE, 'r') as f:
   self.chords = json.load(f, object_pairs_hook=OrderedDict)

We then modify the chords frame GUI to add two combobox (see the complete GUI in 7.05 view.py build_chords_frame):

self.chords_selector = ttk.Combobox(self.chords_frame,  values=[k for k 
  in self.chords.keys()])
self.chords_selector.current(0)
self.chords_selector.bind("<<ComboboxSelected>>", self.on_chord_changed)
self.chords_selector.grid(row=1, column=1, sticky='e', padx=10, 
  pady=10)
self.chords_key_selector = ttk.Combobox(self.chords_frame, values=[k  
  for k in KEYS])
self.chords_key_selector.current(0)
self.chords_key_selector.bind("<<ComboboxSelected>>", self.on_chords_key_changed)

Next, we added the two event callbacks defined previously:

def on_chord_changed(self, event):
  self.remove_all_key_highlights()
  self.find_chord(event)
 
def on_chords_key_changed(self, event):
  self.remove_all_key_highlights()
  self.find_chord(event)

 The find_chord method queries the self.chords dict for the keys to be highlighted, adds the key offsets from the root note, and calls it to be highlighted and played:

def find_chord(self, event=None):
  self.selected_chord = self.chords_selector.get()
  self.chords_selected_key = self.chords_key_selector.get()
  index_of_selected_key = KEYS.index(self.chords_selected_key)
  self.keys_to_highlight = [ ALL_KEYS[i+index_of_selected_key] for 
                         i in self.chords[self.selected_chord]]
  self.highlight_list_of_keys(self.keys_to_highlight)
  play_chord_in_new_thread(self.keys_to_highlight)

The final code in this iteration modifies the on_mode_changed method to highlight the chord as soon as the chord mode is selected:

 def on_mode_changed(self, event):
   self.remove_all_key_highlights()
   selected_mode = self.mode_selector.get()
   if selected_mode == 'Scales':
     self.show_scales_frame()
     self.find_scale()
   elif selected_mode == 'Chords':
     self.show_chords_frame()
     self.find_chord()
   elif selected_mode == 'Chord Progressions':
     self.show_progressions_frame()

That concludes the iteration. If you now run 7.05 view.py, you will find a functional chords section that lets us find chords of different varieties in different scales.