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), ...]

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)

10 Synth Waveforms

sine, saw, triangle, square, pulse, FM, noise, supersaw, PWM slow, PWM fast — with detune, stereo pan, and spread.

58 Drum Patterns

rock, jazz, bebop, bossa nova, salsa, samba, afrobeat, funk, reggae, house, trap, metal, drum and bass — and 45 more. Plus 21 fill presets. 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.

25 Instrument Presets

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

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