Skip to content


Folders and files

Last commit message
Last commit date

Latest commit


Repository files navigation

README for python-ly

This package provides a Python library ly containing various Python modules to parse, manipulate or create documents in LilyPond format. A command line program ly is also provided that can be used to do various manipulations with LilyPond files.

The LilyPond format is a plain text input format that is used by the GNU music typesetter LilyPond (

The python-ly package is Free Software, licensed under the GPL. This package is written by the Frescobaldi developers and is used extensively by the Frescobaldi project. The main author is Wilbert Berendsen.

The ly command line tool

With ly you can reformat, or re-indent LilyPond files, transpose music, translate pitch names, convert LilyPond to syntax-colored HTML, etc.

There is also experimental support for converting LilyPond to MusicXML.


ly -h

to get a full list of the features of the ly command.

Here is an example to re-indent and transpose a LilyPond file:

ly "indent; transpose c d" -o

To test the ly module from the current directory without installing, use:

python -m ly <args...>

This will behave like running the ly command when the package is installed.

The ly Python module

The ly module supports both Python2 and Python3. This is a short description of some modules:

  • ly.slexer: generic tools to build parsers using regular expressions
  • ly.node: a generic list-like node object to build tree structures with
  • ly.document: a tokenized text document (LilyPond file)
  • ly.lex: a parser for LilyPond, Scheme, and other formats, using slexer
  • a tree structure of the contents of a document
  • ly.pitch: functions for translating, transposing etc
  • ly.indent: indent LilyPond text
  • ly.reformat: format LilyPond text
  • ly.dom: (deprecated) tree structure to build LilyPond text from
  • ly.words: words for highlighting and autocompletion
  • layout objects, properties, interfaces, font glyphs etc extracted from LilyPond


The documentation is built using Sphinx and located in the doc directory. If you have Sphinx installed, you can build nicely formatted HTML documentation by typing make html in the doc directory.

You can also read the docs online at