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

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 4.4 (Luna) 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, download the version that complies with your system. If in doubt, 32-bit is a safe option, as 64-bit systems are back-compatible to 32-bit programs.

For Mac users, once the .tar file has been unzipped, drag the ‘eclipse’ folder into the Applications folder in your dock (make sure to drag the folder and not just the Eclipse icon - there are libraries and other dependencies that need to be kept together).


Once done, click on the Eclipse icon in the eclipse folder, and it should load.


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.

Installing for 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 and EGit 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 may next need to install two plugins: PyDev and EGit. The Eclipse for Java EE has some of these installed.

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 3.5)

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

  4. Search for EGit in the Marketplace search box, and click Install in the proper search results:

  5. Now, when asked to confirm the installation of both PyDev and EGit, click Confirm:

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

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

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



The 3.x series of PyDev - currently available in the Eclipse Marketplace - requires Java 7. The plugin will not activate in Eclipse without Java 7. If you are unable or unwilling to install Java 7, uninstall your PyDev 3.x plugin via the Eclipse Marketplace dialog, and install a copy of PyDev from the 2.x series manually.

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 Configuring Environment Settings for more information on configuring user settings. Otherwise, head to: usersGuide_00_introduction for further demos and tutorials on using music21.

Committing, pushing and pulling in Eclipse

Git differs from the previous repository software of music21 (subversion/SVN) in a lot of ways, and one of the biggest is in how each handles committing changes.

In SVN, making a commit both updates the history in your local copy of the repository and sends those changes up to the central server for that repository.

In Git, these actions are broken into smaller discrete steps:

  1. Add modifications in your working directory to the “staging area” - the list of changes you intend to bundle into a commit.
  2. Make a commit out of the “staged changes”. Now the history of your local repository has changed. You can repeat steps one and two to make as many commits as you like.
  3. Push your commits to the central server. If you’ve changed files that someone else was working on, you may be obliged to merge, but Git makes that relatively painless. After pushing, all of your local commits will be added to the history in the central server for others to fetch.

Likewise, in SVN, updating takes the current state of the central server and both updates the history in your local copy and changes the files and directories present there - adding, deleting or modifying the contents of your working directory.

Again, in Git, these actions are broken into smaller discrete steps:

  1. Fetch history from the central server. Now you can see how the history in your local repository differs from the history upstream - the changes that everyone else has been making.
  2. If you like what you see, you can pull to update your working directory to be the same as the most recent change from upstream. You can also pull from any point in the history of the repository. Git is incredibly flexible, but also potentially intimidating for the same reason.

Eclipse with EGit makes much of this simple. You’ll probably never have to worry about most of Git’s advanced features - branching, rebasing, etc.

Adding changes, committing and pushing

There are two ways to commit changes. Either download the GitHub application for your operating system (recommended) and follow the instructions there, or use these instructions to commit directly from Eclipse. I strongly recommend the former.

  1. To add changes to Git’s “staging area”, right-click in Eclipse’s Project Explorer on the music21 project folder and select Add to Index from the Team submenu:


    Files and folders with changes staged for commit will appear with a little asterisk in the Project Explorer.

  2. To make a commit, right-click in Eclipse’s Project Explorer on the music21 project folder and select Commit... from the Team submenu:

  3. Now you can write a commit message in the Commit Changes dialog box. You can also refine which modifications you want included in the commit by selecting and deselecting files in the Files list at the bottom of the dialog box.

    When you’re happy with the commit message, click on either Commit or Commit and Push. The first option will simply add the commit to your local history, while the second option will both commit to your local history and then send that history up to GitHub. In the rare occurance that you have a merge conflict (for example, if you’ve been developing on different computers with slightly different history on each), Eclipse will help you merge before pushing:


Fetching and pulling in Eclipse

Fetching and pulling in Eclipse can be easier for most people than committing and pushing. Just right-click on the music21 project folder in Eclipse’s Project Explorer and select either Pull to pull or Fetch from Upstream to fetch from your fork on GitHub.

Some people have had major problems with this system, however, so there’s an alternate way described below.

Fetching and pulling via the GitHub app

This is possible but a little bit harder. See this post I made, , for information. Replace all references to “mk270/master” to “cuthbertLab/master” and it should make sense.

Configurating Git remotes in Eclipse

By default, your local copy of music21 knows about your fork on GitHub. When you commit and push changes, those changes go to your fork. And when you fetch history and pull changes, those changes come from your fork.

However, Git repositories can be taught about other remote repositories, otherwise known as remotes. This is important, because the changes that are made to the official music21 repository will not be automatically propagated to your fork. You need to teach your fork about the official repository, and fetch those changes into your forks history manually.

Luckily, configuring Git remotes in Eclipse is easy.

  1. First, right-click on your music21 project in Eclipse’s Project Explorer view. Select Show in Repositories View from the Team submenu:

  2. In the Repositories View you’ll find the various Git repositories on your system that Eclipse is aware of. Underneath music21, you’ll find sections titled Branches, Tags, References, Remotes and Working Directory. Right-click on Remotes and select Create Remote...:

  3. In the New Remote dialog, choose the remote name upstream, and select Configure fetch. The name upstream is used in Git parlance to indicate the official repository from which your repository was forked. Once you’ve entered the correct information, click OK:

  4. In the Configure Fetch dialog, click Change:

  5. Now, enter the information for the official music21 repository -, as well as your GitHub credentials, and click Finish. Eclipse will fill in the other boxes for you:

  6. Back in the Configure Fetch dialog, just click Save. You’ve now configured your local copy to know about both your fork on GitHub and the official music21 fork:


Fetching from upstream

Once you’ve configured an upstream remote, you can fetch history from the official music21 repository.

  1. Right-click on your music21 project in Eclipse’s Project Explorer and select Team > Remote > Fetch from...:

  2. In the Fetch from Another Repository dialog, choose the upstream remote from the Configured remote repository drop-down menu, then press Finish:

  3. If there were any changes in the official repository, you’ll see them come in now:



With Git, fetching history (from your own fork, or from another remote) does not change the contents of your working directory.

After fetching, you need to pull in order for that history to be reflected in your working directory.

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 (not through Eclipse). 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.