1CHROMATIC_SCALE = (
  2    'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'
  3)
  4
  5TONES_COUNT = 12
  6MINOR_THIRD_LEN = 3
  7MAJOR_THIRD_LEN = 4
  8
  9
 10class Tone:
 11
 12    def __init__(self, tone_name):
 13        self.tone_name = tone_name
 14
 15    def __str__(self):
 16        return self.tone_name
 17
 18    def __eq__(self, other):
 19        return self.tone_name == other.tone_name
 20
 21    def __ne__(self, other):
 22        return self.tone_name != other.tone_name
 23
 24    def __add__(self, other):
 25        if isinstance(other, Tone):
 26            return Chord(self,other)
 27        elif isinstance(other, Interval):
 28            new_tone_idx = (CHROMATIC_SCALE.index(self.tone_name) + other.semitones_count) % TONES_COUNT
 29            return Tone(CHROMATIC_SCALE[new_tone_idx])
 30
 31    def __sub__(self, other):
 32        if isinstance(other, Tone):
 33            self_idx = CHROMATIC_SCALE.index(self.tone_name)
 34            other_idx = CHROMATIC_SCALE.index(other.tone_name)
 35            interval_length = (self_idx - other_idx) % TONES_COUNT
 36            return Interval(interval_length)
 37        elif isinstance(other, Interval):
 38            new_tone_idx = (CHROMATIC_SCALE.index(self.tone_name) - other.semitones_count) % TONES_COUNT
 39            return Tone(CHROMATIC_SCALE[new_tone_idx])
 40
 41
 42class Interval:
 43
 44    _INTERVAL_NAMES = (
 45        'unison', 'minor 2nd', 'major 2nd', 'minor 3rd', 'major 3rd',
 46        'perfect 4th', 'diminished 5th', 'perfect 5th', 'minor 6th',
 47        'major 6th', 'minor 7th', 'major 7th'
 48    )
 49
 50    def __init__(self, semitones_count):
 51        self.semitones_count = semitones_count
 52
 53    def __str__(self):
 54        return self._INTERVAL_NAMES[self.semitones_count % TONES_COUNT]
 55
 56    def __add__(self, other):
 57        if isinstance(other, Tone):
 58            raise TypeError('Invalid operation')
 59        elif isinstance(other, Interval):
 60            new_count = (self.semitones_count + other.semitones_count)
 61            return Interval(new_count)
 62
 63    def __sub__(self, other):
 64        if isinstance(other, Tone):
 65            raise TypeError('Invalid operation')
 66
 67    def __neg__(self):
 68        return Interval(-self.semitones_count)
 69
 70
 71class Chord:
 72
 73    def __init__(self, *tones):
 74        if not self._are_valid_tones(*tones):
 75            raise TypeError('Cannot have a chord made of only 1 unique tone')
 76        self.sorted_tones = self._sort_tones(*tones)
 77
 78    @staticmethod
 79    def _are_valid_tones(*tones):
 80        tones_set = {str(tone) for tone in tones}
 81        return len(tones_set) > 1
 82
 83    @staticmethod
 84    def _sort_tones(*tones):
 85        root = tones[0]
 86        sorted_tones = [root]
 87        end_idx = CHROMATIC_SCALE.index(str(root))
 88        iter_idx = (end_idx + 1) % TONES_COUNT
 89
 90        while iter_idx != end_idx:
 91            current_tone = Tone(CHROMATIC_SCALE[iter_idx])
 92            if current_tone in tones and current_tone not in sorted_tones:
 93                sorted_tones.append(current_tone)
 94            iter_idx += 1
 95            iter_idx %= TONES_COUNT
 96        return sorted_tones
 97
 98    def __str__(self):
 99        return '-'.join(str(tone) for tone in self.sorted_tones)
100
101    def is_minor(self):
102        root_idx = CHROMATIC_SCALE.index(str(self.sorted_tones[0]))
103        end_tone_idx = (root_idx + MINOR_THIRD_LEN) % TONES_COUNT
104        return Tone(CHROMATIC_SCALE[end_tone_idx]) in self.sorted_tones
105
106    def is_major(self):
107        root_idx =  CHROMATIC_SCALE.index(str(self.sorted_tones[0]))
108        end_tone_idx = (root_idx + MAJOR_THIRD_LEN) % TONES_COUNT
109        return Tone(CHROMATIC_SCALE[end_tone_idx]) in self.sorted_tones
110
111    def is_power_chord(self):
112        return not self.is_minor() and not self.is_major()
113
114    def __add__(self, other):
115        if isinstance(other, Tone):
116            new_tones = self.sorted_tones + [other]
117            return Chord(*new_tones)
118        elif isinstance(other, Chord):
119            new_tones = self.sorted_tones[:]
120            new_tones.extend(other.sorted_tones)
121            return Chord(*new_tones)
122
123    def __sub__(self, other):
124        if isinstance(other, Tone):
125            if other not in self.sorted_tones:
126                raise TypeError(f'Cannot remove tone {str(other)} from chord {str(self)}')
127            new_tones = self.sorted_tones[:]
128            new_tones.remove(other)
129            return Chord(*new_tones)
130
131    def transposed(self, interval):
132        transpose = lambda tone : tone + interval
133        transposed_tones  = list(map(transpose, self.sorted_tones))
134        return Chord(*transposed_tones)