capo 0.6

Capo: A Python Library for Guitar Chord Transposition

Capo: A Python Library for Guitar Chord Transposition

Overview

Capo is a lightweight Python library for guitarists and developers that provides precise chord transposition across capo positions. It allows users to easily convert chord progressions from one capo setting to another, supporting sharps, flats, complex chord types, and slash chords. Whether you’re building a songwriting assistant, a practice tool, or a music theory application, Capo delivers a clear, reliable foundation for working with chord mappings and capo calculations in Python.

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Installation

Source Code

• Download Version 0.6 or Latest Source
• pip install .

PyPI

• Check Python Packaging User Guide
• pip install capo==0.6

Usage

Capo Map

Automatically converts chords between different capo positions while preserving harmonic relationships.

>>> from capo import capo_map
>>> capo_map(["A", "Em", "C", "G"], target_capo=2, current_capo=0)
['G', 'Dm', 'A#', 'F']
>>> capo_map(["A", "Em", "C", "G"], target_capo=2, current_capo=0, flat_mode=True)
['G', 'Dm', 'Bb', 'F']

Transpose

Shifts chords up or down by a specified number of semitones to change the song's key.

>>> from capo import transpose
>>> transpose(["A", "E", "Cm", "G", "Fmaj7"], semitones=3)
['C', 'G', 'D#m', 'A#', 'G#maj7']
>>> transpose(["A", "E", "Cm", "G", "Fmaj7"], semitones=3, flat_mode=True)
['C', 'G', 'Ebm', 'Bb', 'Abmaj7']

Key Scores

Returns all possible keys and their corresponding scores for a given list of chords using the Krumhansl-Schmuckler algorithm.

>>> from capo import key_scores
>>> key_scores(["Em", "Am", "G", "Bm", "Em", "C", "G", "Bm", "Em"])
{'A#m': 0.4871417233740239, 'G#': 0.4774543026320962, 'A#': 0.5520334829280494, 'D': 0.7477367635967468, 'Am': 0.6716505683174476, 'Gm': 0.6750401588831327, 'A': 0.6622255631674839, 'Dm': 0.6367313900369936, 'G': 0.8399547248439911, 'F#m': 0.6173531647275109, 'Fm': 0.530630809877153, 'C#m': 0.5987423938857308, 'D#': 0.5377480823857491, 'C': 0.7278176839673419, 'F#': 0.5572647563660749, 'F': 0.5820127037844264, 'Em': 0.8254612345527799, 'C#': 0.4563950736636346, 'E': 0.7179587455649095, 'B': 0.7088375508524547, 'G#m': 0.6478594798186766, 'D#m': 0.564206942839128, 'Cm': 0.6280335727363678, 'Bm': 0.8030131913724882}
>>> key_scores(["G#", "G#", "Fm", "C#", "D#", "G#", "Fm", "C#", "D#"], flat_mode=True)
{'Cbm': 0.5059430034954594, 'D': 0.47214060767880817, 'Fbm': 0.5663422985823668, 'Am': 0.626082212718544, 'Gm': 0.6473142793320639, 'Gb': 0.6249570609550481, 'Dm': 0.5984541508829389, 'G': 0.5502083795108782, 'Fm': 0.8274571550716174, 'Dbm': 0.6608315888220377, 'Bbm': 0.7017791458623973, 'Abm': 0.7402210552899815, 'Ab': 0.8839844066440953, 'Bb': 0.6867751194296899, 'Ebm': 0.6941303268339243, 'Db': 0.7655343684259058, 'F': 0.6847698356536668, 'Fb': 0.573580307659009, 'Gbm': 0.5507809081451287, 'Eb': 0.8043262373344897, 'Cb': 0.5963990540758232, 'C': 0.6631957481323153, 'Cm': 0.8049063265566369, 'A': 0.4962731607074994}

Detect Key

Automatically identifies the musical key from a sequence of chords using the Krumhansl-Schmuckler algorithm.

>>> from capo import detect_key
>>> detect_key(["Em", "Am", "G", "Bm", "Em", "C", "G", "Bm", "Em"])
'G'
>>> detect_key(["G#", "G#", "Fm", "C#", "D#", "G#", "Fm", "C#", "D#"], flat_mode=True)
'Ab'

Transpose to Key

Automatically transposes a list of chords from their current key to a target key.
If the current key is not provided, it will be detected automatically.

⚠️ Chords are shifted chromatically; chord qualities are not adjusted to the target key's scale.

>>> from capo import transpose_to_key
>>> transpose_to_key(["Am", "F", "C", "G"], target_key="C")
['Em', 'C', 'G', 'D']
>>> transpose_to_key(["Am", "F", "C", "G"], current_key="A", target_key="C")
['Cm', 'G#', 'D#', 'A#']
>>> transpose_to_key(["Am", "F", "C", "G"], current_key="A", target_key="C", flat_mode=True)
['Cm', 'Ab', 'Eb', 'Bb']

Issues & Bug Reports

Just fill an issue and describe it. We'll check it ASAP!

• Please complete the issue template

References

1- Guitar chords capo calculator - GuitarPlayerBox

2- Enharmonic Equivalents - Music Theory Academy

3- Capo Calculator

4- Chord Transposer: Online Tool to Transpose Chords

5- Enharmonic Equivalent Chart with Enharmonic Note Names

6- Schmuckler, M.A., 1989. Expectation in music: Investigation of melodic and harmonic processes. Music Perception, 7(2), pp.109-149.

7- Chord Interval Chart: How Chords Are made (Notes and Interval Formulas)

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Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog and this project adheres to Semantic Versioning.

Unreleased

0.6 - 2026-01-05

Added

• key_scores function

Changed

• detect_key function modified
• README.md updated
• Test system modified

0.5 - 2025-12-15

Added

• transpose_to_key function

Changed

• capo_map function modified
• README.md updated
• Test system modified

0.4 - 2025-12-05

Added

• detect_key function

Changed

• _validate_chords function modified
• README.md updated
• Test system modified

0.3 - 2025-11-26

Added

• Double sharp notes
• Double flat notes

Changed

• Fb bug fixed
• Cb bug fixed
• E# bug fixed
• B# bug fixed
• README.md updated
• Test system modified

0.2 - 2025-11-15

Added

• transpose function
• Logo

Changed

• README.md updated
• capo_map function modified
• Test system modified

0.1 - 2025-11-05

Added

• capo_map function
• Flat notes
• Sharp notes