chord-lab-with-pytheory

Chord Lab

Everything about a single chord — construction, voicing, and analysis.

Build a chord

from pytheory import Chord

Chord.from_symbol("F#m7b5")     # widest parser: sus, add9, alterations, slash
Chord.from_name("Am")           # plain names (major/minor/7/maj7/dim/…)
Chord.from_intervals("C", 0, 4, 7)   # root + semitone intervals
Chord.from_tones("C", "E", "G")      # explicit notes

A Chord has .symbol, .tones (list of Tone), .root, and .transpose(semitones).

Voicings

inversion, drop2, drop3, and open_voicing return a new Chord. The chord symbol stays the same — the change is in the tones (order/octave), so inspect .tones:

c = Chord.from_symbol("Cmaj7")
[str(t) for t in c.tones]                  # ['C4', 'E4', 'G4', 'B4']
[str(t) for t in c.inversion(1).tones]     # ['E4', 'G4', 'B4', 'C5']
[str(t) for t in c.drop2().tones]          # ['G3', 'C4', 'E4', 'B4']
[str(t) for t in c.open_voicing().tones]   # ['C4', 'E5', 'G4', 'B5']

drop3() exists too. Use these to spread a close voicing for piano/strings/guitar.

Analysis

c = Chord.from_symbol("Cmaj7")

c.intervals            # [4, 3, 4]   semitone steps between stacked tones
c.pitch_classes        # {0, 4, 7, 11}
c.forte_number         # '4-20'      set-theory label
c.figured_bass         # '7'
c.extensions()         # [<Tone D5>, <Tone A5>]   available 9/11/13 tones
c.tension              # {'score': 0.15, 'tritones': 0, 'minor_seconds': 1,
                       #  'has_dominant_function': False}
c.dissonance           # 5.33  (a roughness number; higher = more dissonant)
c.beat_frequencies     # [(Tone, Tone, hz), …]  beating between pairs in ET

Pitch-class-set toolkit

c = Chord.from_symbol("Cmaj7")

c.normal_form          # (11, 0, 4, 7)   most compact ordering
c.prime_form           # (0, 1, 5, 8)    canonical set-class form
c.interval_vector      # (1, 0, 1, 2, 2, 0)  interval-class content <ic1..ic6>
c.complement           # Chord of the other 8 pitch classes

# Set-class relationships between two chords:
Chord.from_symbol("C").is_transposition_of(Chord.from_symbol("G"))   # True (Tn)
Chord.from_symbol("C").is_set_class_equivalent(Chord.from_symbol("Cm"))  # True (TnI: maj/min)
Chord.from_symbol("C").is_subset_of(Chord.from_symbol("Cmaj7"))      # True
# Z-relation — same interval vector, different set class (e.g. 4-z15 / 4-z29):
a, b = Chord.from_midi_message(0,1,4,6), Chord.from_midi_message(0,1,3,7)
a.is_z_related(b)      # True