Using music21 with Git for Eclipse

Music21 stores its master code base in the Git code format at the GitHub website ( ). In order to have the latest, unreleased, versions of music21, which often incorporate new bug fixes, users will need to be familiar with Git.

Developers of music21 who want access to support or committing to the code base need to use the IDE called Eclipse, which allows for easy debugging and enforcing of coding standards such as consistent whitespace, no unused variable names, and simple error catching. Thus, while Eclipse is not strictly necessary to editing the Python files that make up music21, it is the only supported environment for receiving technical assistance. Thus students and others who wish to be part of the development team for music21 will need to follow the instructions below on using Git for Eclipse.


Installing Git

First, make sure you have Git installed. You can find binaries for Windows, OSX and Unix at

But the best way to do almost everything with Git and music21 today is with the GitHub Desktop app, at <>.

Installing Eclipse

Once you have Git installed, download and install Eclipse. You can find the most recent version of Eclipse for Java EE at, and these instructions are written with Eclipse for Java EE 4.8 (Oxygen) in mind though some screenshots are from 4.3 (Kepler).

Installing for Windows

For Windows users, the safest bet is the 32-bit version, regardless of your system’s capabilities.

If you download the 32-bit version save the Eclipse folder within the zip file in your “Program Files (x86)” directory if there is one, or “Program Files” if there isn’t.

If you choose the 64-bit version (getting more stable) then put the folder in the “Program Files” directory even if there is an “(x86)” directory. You may need to give permission or your password to make this copy.

After you’ve put the folder, go into the folder and drag a shortcut (by holding down Alt when dragging) to Eclipse to your start menu (or know how to find it later).

If you try running Eclipse and it gives you a warning about not having Java installed, go to and download a copy there.

Installing for Mac

For Mac users, unless your computer is very old, download the 64-bit Java EE system.

For Mac users, once the .tar file has been unzipped, drag the ‘eclipse’ app. into the Applications folder in your Finder. Once done, click on the Eclipse icon.

You’ll be prompted to select a workspace directory, which, by default is created in your documents folder. Be sure to remember where this directory is, as it is where music21 will be installed. I use ‘/Users/cuthbert/git’ for my workspace (you probably wouldn’t use cuthbert).

If you get an error about Java being too old, download a new one from

Installing for GNU/Linux/FreeBSD/Unix

You’ve chosen to run Unix – you should be able to figure this out on your own. :-)

Because there are so many slightly incompatible flavors of UNIX, the music21 team provides free support for problems arising with Windows and Mac installations only; UNIX users have saved a few hundred dollars by running a free OS and can spend their savings on paid support.

Installing PyDev for Eclipse


If you are using Windows, make sure to install Python through the normal Windows installation routines. See Installing music21 in Windows.


If you are using Windows and have a firewall or anti-virus software active, we recommend disabling them while installing Eclipse plugins. Anti-virus software, such as AVG, can cause Eclipse to hang while attempting to fetch packages.

With Eclipse installed, you next need to install the plugin PyDev.

PyDev is a Python IDE for Eclipse, which may be used in Python, Jython, and IronPython development. EGit is a plugin that allows Eclipse to work with Git repositories. Both of these can be installed via the Eclipse Marketplace.

  1. Launch the Eclipse Marketplace via Eclipse’s Help menu:

  2. Search for PyDev in the Marketplace search box, and click Install in the proper search results: (the latest version is now 5.9)

  3. When asked to confirm the installation, click Continue to return to the search dialog:

  4. Now, when asked to confirm the installation of PyDev, click Confirm (note: your system probably won’t also have “EGit” listed).

  5. You will be asked to accept the licensing for the plugin. Choose “I accept the terms of the license agreements” and click Finish:

  6. Eclipse will now go through the process of automatically installing the plugin. When it finishes, you’ll be asked to confirm the certificate for PyDev. Click the checkbox and press OK:

  7. Finally, Eclipse will ask to restart. Click Yes to complete the plugin installation process:


Forking music21 on GitHub

The main development paradigm in Git is to create a “Fork” or individualized copy of the music21 code base under your own name and make modifications there. You may “Pull” changes that we have made to the main music21 version into your own fork so that your fork stays up to date. If you’d like to contribute your changes back to the main codebase, you will initiate something called a “pull request” later.

To fork the official music21 repository, simply navigate to on GitHub while signed in to your GitHub account, and click Fork in the upper right-hand corner of the page.


Cloning your music21 fork in Eclipse

Once you’ve forked music21 on GitHub, you need to clone your fork locally to your machine in order to start working.

To start the cloning process, choose Import… from Eclipse’s File menu, or right-click in the Package Explorer and choose Import from the contextual menu that appears.

  1. In the Import dialog, open the Git folder and select Projects from Git, then click Next:


    You may not see the “Repositories from GitHub” option on your computer. That’s okay, despite using GitHub, you won’t actually use this option.

  2. You’ll now be asked to choose a repository source. While you can try using the GitHub repository source - which allows dynamically searching GitHub for repositories - if you’ve just made your fork a few minutes ago it won’t show up when searching. We recommend selecting the Clone URI option. Once you’ve selected Clone URI, click Next:

  3. Now you need to enter information about your fork. For the purposes of this tutorial, we’ll use the fork of music21 found at, but take note of the information for your own fork when proceeding here. The GitHub webpage lists the clone URL for this fork partway-down the right side of the page. The HTTPS clone URL for this fork is

    Enter the GitHub clone URL into the URI field in the Location section of Eclipse’s dialog, then enter your GitHub credentials in the Authentication section. The other fields will be filled in automatically, and you don’t need to touch them.

    When finished, press Next:

  4. In the Branch Selection dialog, simply click Next:

  5. In the Location Destination dialog, you can choose the local destination for the repository. By default, Eclipse will try and clone new repositories into a git folder in your home directory. In the example below, we’re opting to put it somewhere else.

    Choose a new directory, or accept Eclipse’s default. Then, click Next:

  6. Eclipse is now cloning your music21 fork! Sit tight: this will take a few minutes:

  7. Once the cloning process has finished, click Next in the following dialog:

  8. Finally, you’ll be given the option to choose how Eclipse will refer to the project. Choose music21base instead of music21.


    You can name your music21 Eclipse project whatever you like. However, we strongly recommend choosing a project name other than music21. Why? The project you’ve now downloaded contains a directory named music21. You may run into problems if you create subsequent projects in Eclipse which attempt to reference the music21 Python package inside the music21 Eclipse project. Naming the Eclipse project to something other than music21 mitigates this reference problem.


Configuring your music21 project with PyDev

You need to teach Eclipse that music21 should be considered a PyDev project. In the Package Explorer window, right-click on your music21 project and choose Set as PyDev Project from the PyDev submenu:


If you don’t see this option, see

You also need to tell PyDev that your project should be included in your Python path. If you don’t do this, Python won’t be able to find music21 at all.


Configuring the music21 Environment

Configuring the music21 Environment is done mostly like a normal install with one big difference noted below.

To create a user environment settings file, open the music21/ file and run it by pressing the green circle with a white arrowhead in it at the top of the Eclipse interface.


A new “Run As” window will appear in which you will be prompted to select a way to run Choose “Python Run” and click on “OK.” (You should always click this when running Python programs)


In the console, you may see errors about installing additional packages, after which you will see a message beginning with “Welcome to the music21 Configuration Assistant.”


When asked if you would like to install music21 in the normal place for Python packages, type no and press Enter.


Make sure you write no here.


See User’s Guide, Chapter 24 for more information on configuring user settings. Otherwise, head to: What is Music21? for further demos and tutorials on using music21.

Committing, pushing and pulling

This used to be really hard…now look at the instructions for the Github Desktop app.

Sending pull requests to the official music21 repository

To get your changes into the official music21 repository, you’ll have to make a pull request via the GitHub web site or the desktop app.

A pull request is just what it sounds like: a request to another repository (the music21 team’s copy) for them to pull in changes from your repository and add them to the centralized version.

Making pull requests is easy:

  1. Log into GitHub and find your fork of music21. Under the repository summary header you’ll see a green button with two arrows, labeled “Compare & review”.

    Click that button:

  2. If your repository differs from the official music21 repository, you’ll be shown the diff stats, as well as a large banner with the text Click to create a pull request for this comparison.

    Click on that banner to continue:

  3. Almost done. Now you can write a description of what your pull request involves. While the music21 team can and will review the diffs for your request, please provide a useful description. What do your changes accomplish? Do they address one of the issues in the official issue tracker? Which issue? Do they represent an enhancement, or new functionality?

    When you’ve finished writing your description, click on the Send pull request button. You’ve sent your pull pull request!


Getting your pull requests accepted

Once you’ve sent a pull request to the music21 team they’ll need to review the changes you’ve suggested. They can opt to accept some, all or none of the commits you’ve included in your pull request. If the work looks good, they’ll merge your changes into the official repository.

What do we mean by the “if the work looks good”? The first and highest priority is that if the code expands music21 in any way that it is well documented (see Documenting music21) and includes tests that ensure that future changes to the system will not break the code. You will need to run test/ which will update the file test/lastResults.txt to show that the tests have passed. To run these tests you will need to install the optional modules such as NumPy, matplotlib, etc. The tests you have written cannot add appreciatively to the amount of time it takes to run the test suite (so a few milliseconds for a tiny addition, at most a second or two for a major contribution). The code needs to be well placed within the structure of the library so as not to add unneeded complexity. For instance, if your new methods will only apply to a small number of users working on a constrained repertory (such as chorales, jazz, medieval music, etc.) it should not add ten new methods to Note or Stream. The contributions cannot require any new external dependencies and even optional dependencies should be discussed with the music21 team before attempting a Pull Request. The code should work on Mac, Windows (watch out for file system calls), and Unix equally well. It sounds hard, but after a while looking out for these caveats becomes second nature and will help ensure the toolkit is viable for at least a decade to come.