1INVALID_OPERATION_MESSAGE = "Invalid operation"
  2
  3
  4class Tone(str):
  5    """Class that represents a musical tone."""
  6    TONES = ('C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B')
  7
  8    def __add__(self, other):
  9        """Add two tones or an interval to a tone."""
 10        if isinstance(other, Tone):
 11            return Chord(self, other)
 12        if isinstance(other, Interval):
 13            current = self.TONES.index(self)
 14            new = self.TONES[(current + int(other)) % len(self.TONES)]
 15            return Tone(new)
 16
 17    def __sub__(self, other):
 18        """Subtract two tones or an interval from a tone."""
 19        if isinstance(other, Tone):
 20            return Interval(self.TONES.index(self) - self.TONES.index(other))
 21        if isinstance(other, Interval):
 22            return self.__add__(-other)
 23
 24    def __radd__(self, other):
 25        """Raise an exception attempting right-hand addition."""
 26        raise TypeError(INVALID_OPERATION_MESSAGE)
 27
 28    __rsub__ = __radd__
 29
 30
 31class Interval:
 32    """Class that represents a musical interval."""
 33    INTERVAL_NAMES = (
 34        "unison",
 35        "minor 2nd",
 36        "major 2nd",
 37        "minor 3rd",
 38        "major 3rd",
 39        "perfect 4th",
 40        "diminished 5th",
 41        "perfect 5th",
 42        "minor 6th",
 43        "major 6th",
 44        "minor 7th",
 45        "major 7th"
 46    )
 47
 48    def __init__(self, value):
 49        """Save the normalized initialization value for the interval."""
 50        self._value = value % len(self.INTERVAL_NAMES)
 51
 52    def __str__(self):
 53        return self.INTERVAL_NAMES[self._value]
 54
 55    def __add__(self, other):
 56        """Add two intervals or raise an error if adding anything else to an interval."""
 57        if isinstance(other, Interval):
 58            return Interval(self._value + other._value)
 59        raise TypeError(INVALID_OPERATION_MESSAGE)
 60
 61    def __neg__(self):
 62        return Interval(-self._value)
 63
 64    def __int__(self):
 65        return self._value
 66
 67
 68class Chord:
 69    """Class that represents a musical chord."""
 70    CANNOT_CHORD_CHORD_MESSAGE = "Cannot have a chord made of only 1 unique tone"
 71    CANNOT_REMOVE_TONE_MESSAGE = "Cannot remove tone {0} from chord {1}"
 72
 73    def __init__(self, *notes):
 74        """Leave only unique notes and sort relative to the root."""
 75        root = notes[0]
 76        unique_and_sorted = sorted(list(set(notes)))
 77        root_index = unique_and_sorted.index(root)
 78        unique_and_sorted = unique_and_sorted[root_index:] + unique_and_sorted[:root_index]
 79        if len(unique_and_sorted) <= 1:
 80            raise TypeError(self.CANNOT_CHORD_CHORD_MESSAGE)
 81        self.notes = unique_and_sorted
 82
 83    def __str__(self):
 84        return "-".join(self.notes)
 85
 86    def __add__(self, other):
 87        """Add a tone to a chord."""
 88        if isinstance(other, Tone):
 89            return Chord(*self.notes, other)
 90        if isinstance(other, Chord):
 91            return Chord(*self.notes, *other.notes)
 92
 93    def __sub__(self, other):
 94        """Remove a tone from a chord if possible."""
 95        if isinstance(other, Tone):
 96            if other not in self.notes:
 97                raise TypeError(self.CANNOT_REMOVE_TONE_MESSAGE.format(other, self))
 98            return Chord(*[note for note in self.notes if note != other])
 99
100    def is_minor(self):
101        """Determine the age of the chord."""
102        return (Tone(self.notes[0]) + Interval(3)) in self.notes
103
104    def is_major(self):
105        """Determine the military rank of the chord."""
106        return (Tone(self.notes[0]) + Interval(4)) in self.notes
107
108    def is_power_chord(self):
109        """Determine the strenght of the chord."""
110        return not (self.is_minor() or self.is_major())
111
112    def transposed(self, interval):
113        """Return a new chord with different tones, I'm tired of docstrings."""
114        new_notes = [note + interval for note in self.notes]
115        return Chord(*new_notes)