PyTheory: Music Theory for Humans

Explore music theory, compose multi-part arrangements, and export to MIDI — all in Python.

$ pip install pytheory

Sketch Ideas Fast

from pytheory import Score, Pattern, Key, Duration, Chord
from pytheory.play import play_score

score = Score("4/4", bpm=140)
score.drums("bossa nova", repeats=4)

chords = score.part("chords", synth="fm", envelope="pad", reverb=0.4)
lead = score.part("lead", synth="saw", envelope="pluck", delay=0.3, lowpass=3000)
bass = score.part("bass", synth="sine", lowpass=500)

for sym in ["Am", "Dm", "E7", "Am"]:
    chords.add(Chord.from_symbol(sym), Duration.WHOLE)
    chords.add(Chord.from_symbol(sym), Duration.WHOLE)

lead.arpeggio("Am", bars=2, pattern="updown", octaves=2)
lead.arpeggio("Dm", bars=2, pattern="updown", octaves=2)
lead.set(lowpass=5000, reverb=0.4)
lead.arpeggio("E7", bars=2, pattern="up", octaves=2)
lead.arpeggio("Am", bars=2, pattern="updown", octaves=2)

for n in ["A2", "E2", "A2", "C3"] * 4:
    bass.add(n, Duration.QUARTER)

play_score(score)              # hear it now
score.save_midi("sketch.mid")  # open in your DAW

Hear It Instantly

$ pytheory demo

Music Theory

>>> from pytheory import Key, Chord, Tone

>>> Key("C", "major").chords
['C major', 'D minor', 'E minor', 'F major', 'G major', 'A minor', 'B diminished']

>>> [c.symbol for c in Key("G", "major").progression("I", "V", "vi", "IV")]
['G', 'D', 'Em', 'C']

>>> Chord.from_symbol("F#m7b5").identify()
'F# half-diminished 7th'

>>> Tone.from_string("C4").interval_to(Tone.from_string("G4"))
'perfect 5th'

>>> Key("C", "major").pivot_chords(Key("G", "major"))
['A minor', 'B minor', 'C major', 'D major', 'E minor', 'G major']

>>> Chord.from_tones("C", "E", "G").forte_number
'3-11'

>>> from pytheory.scales import Scale
>>> Scale.recommend("C", "Eb", "F", "Gb", "G", "Bb", top=3)
[('C', 'blues', 1.0), ...]

Guitar

Chord fingerings, tabs, and scale diagrams for guitar and 24 other stringed instruments:

>>> from pytheory import Fretboard

>>> print(Fretboard.guitar().tab("Am"))
A minor
E|--x--
A|--0--
D|--2--
G|--2--
B|--1--
e|--0--

>>> Fretboard.guitar().chord("G")
Fingering(E=3, A=2, D=0, G=0, B=0, e=3)

Melodies and basslines render to ASCII tablature with part.to_tab(), and chord charts work in Nashville numbers too.

Composition

score = Score("4/4", bpm=124)
score.drums("house", repeats=16, fill="house", fill_every=8)

pad = score.part("pad", synth="supersaw", envelope="pad",
                 reverb=0.5, chorus=0.3, sidechain=0.85)
lead = score.part("lead", synth="saw", envelope="pluck",
                  legato=True, glide=0.03, humanize=0.3)
bass = score.part("bass", synth="sine", lowpass=300, sidechain=0.7)

# Song structure
score.section("verse")
# ... add notes ...
score.section("chorus")
lead.set(lowpass=5000, reverb=0.3)
# ... add notes ...
score.end_section()

score.repeat("verse")
score.repeat("chorus", times=2)

56 Synth Waveforms

The 10 classics — sine, saw, triangle, square, pulse, FM, noise, supersaw, PWM slow, PWM fast — plus 46 modeled instruments (Rhodes, Wurlitzer, pipe organ, vibraphone, choir, sitar, theremin, and more), with detune, stereo pan, and spread.

100 Drum Patterns

rock, jazz, bebop, bossa nova, salsa, samba, afrobeat, funk, reggae, house, trap, metal, drum and bass — and 87 more. Plus 37 fill presets and 74 synthesized percussion sounds. Stereo panned like a real kit.

6 Effects with Automation

lead = score.part("lead", synth="saw",
                  distortion=0.7, lowpass=1000, lowpass_q=5.0,
                  delay=0.3, reverb=0.4, reverb_type="plate",
                  chorus=0.3)

# Automate mid-song
lead.set(lowpass=4000, distortion=0.9)

# LFO modulation
lead.lfo("lowpass", rate=0.5, min=400, max=3000, bars=8)

Signal chain: distortion → chorus → lowpass → delay → reverb. Sidechain compression. Master bus compressor/limiter. Stereo output.

Convolution Reverb

7 synthetic impulse responses: Taj Mahal (12s), cathedral, plate, spring, cave, parking garage, canyon.

pad = score.part("pad", synth="supersaw",
                 reverb=0.85, reverb_type="taj_mahal")

6 Musical Systems

Western, Indian (Hindustani), Arabic (Maqam), Japanese, Blues/Pentatonic, Javanese Gamelan — 40+ scales.

83 Instrument Presets

Guitar (8 tunings), bass, ukulele, mandolin family, violin family, banjo, harp, oud, sitar, erhu, and more — with chord fingering generation for 25 stringed instruments.

Command Line

$ pytheory repl                            # interactive scratchpad
$ pytheory demo                            # hear a generated track
$ pytheory key G major                     # explore a key
$ pytheory identify Cmaj7                  # analyze a chord symbol
$ pytheory progression C major I V vi IV   # build a progression
$ pytheory midi C major I V vi IV -o out.mid
$ pytheory play Am7 --synth saw --envelope pluck
$ pytheory modes C                         # show all modes
$ pytheory circle C                        # circle of fifths

Why Python?

A DAW is great for tweaking sounds. But when you're thinking about music — code is faster than clicking. Sketch ideas, hear them instantly, export MIDI, finish in your DAW.

Tools like Claude Code can use PyTheory to prototype musical ideas from natural language — "write a bossa nova in A minor with a saw lead and reverb" becomes real, playable music.

Documentation

pytheory.kennethreitz.org