User’s Guide, Chapter 8: Installing MusicXML Readers and File Formats (1)

Music21 can import and export a bunch of different musical data formats.

Pieces in many of these formats are distributed with music21 as part of the corpus module (see music21.corpus); look at List of Works Found in the music21 Corpus to see them all.

In general, to load a file from disk, call music21.converter.parse(), which can handle importing all supported formats. (For complete documentation on file and data formats, see music21.converter.) If you want to convert a file from the corpus just use music21.corpus.parse():

from music21 import *
b = corpus.parse('bach/bwv66.6')
b.show() # I've altered this so it's much shorter than it should be...
../_images/usersGuide_08_installingMusicXML_3_0.png

Okay, so say you’re having some problems seeing things. The first things to ask are:

Once you have one of these three installed, we can move on. (It is possible to use music21 with Lilypond alone, but that’s much harder to get configured properly, so please try this first)

Run this command (after the from music21 import *):

configure.run()

You can say “no” to everything that is “Yes/No”, but make sure that it is finding your copy of MuseScore, Finale, or Sibelius.

Parsing Files in General

You can parse a file on your hard drive by calling music21.converter.parse(). This returns a Score usually, though sometimes Part (for a format that only handles single parts) or Opus (for multiple scores bound together) comes back instead. You won’t do much with that unless you assign it to a variable, such as c:

c = converter.parse('/Users/cuthbert/Desktop/myXML.xml')

If you’re on a PC, one of the things to notice is that you can use forward slashes, as in:

c = converter.parse('C:/Users/cuthbert/Desktop/myXML.xml')

Or you can use backslashes, as long as you put an r before the quote before the file name:

c = converter.parse(r'C:\Users\cuthbert\Desktop\myXML.xml')

If you’re in the directory of the file, you can just use the local filename (for instance if you start in /Users/cuthbert/ you could just use 'Desktop/myXML.xml'.

If the file you want is on the web, we can give a URL to the music21.converter.parse() function that points to the desired file. Assuming proper system configuration (see Configuring Environment Settings), the file will be downloaded and parsed.

url = 'http://kern.ccarh.org/cgi-bin/ksdata?l=cc/bach/cello&file=bwv1007-01.krn&f=xml'
sAlt = converter.parse(url)
sAlt.measures(1, 5).show() # show first 5 measures
../_images/usersGuide_08_installingMusicXML_16_0.png

Usually, the file format can be guessed from the filename, but if the filename does not have a suffix (Damn you, OS X!) or the URL has the wrong suffix, you can give a format="FORMAT" parameter to the file:

c = converter.parse('/Users/cuthbert/Desktop/myXML', format='musicxml')

One of the things you’ll notice over time is that once you parse a file into music21 once, the next time you parse it it’ll be between 2 and 5 times faster. That’s because we save an optimized version of the file the first time you create a file, and subsequent times you open it it will check to see if the original file has changed, and if it hasn’t, it will read the optimized version instead.

For most people, this will work 100% of the time. But if you’ve done something sneaky (like changed the file without changing its modification time) or you’ve changed the format of the music21 parser, or if something’s not right, or if you just want to do things slower, you can put a forceSource=True keyword into the parse format.

c = converter.parse('/Users/cuthbert/Desktop/myXML.xml', forceSource=True)

By the way...if you’ve read any really old music21 publications, you might see parseWork mentioned instead of parse. It’s the same thing, so anywhere you see parseWork, type parse instead.

File types available to music21

Music21 can read and write a lot of different file formats. Some of them are pretty obscure. Some of them are world standards. The converter module’s capital-c-Converter object can give a list of some of them. Each tool to work with one format is called a subConverter. Here are the formats that music21 can read:

converter.Converter().subconvertersList('input')
 [music21.converter.subConverters.ConverterABC,
  music21.converter.subConverters.ConverterCapella,
  music21.converter.subConverters.ConverterClercqTemperley,
  music21.converter.subConverters.ConverterHumdrum,
  music21.converter.subConverters.ConverterMEI,
  music21.converter.subConverters.ConverterMidi,
  music21.converter.subConverters.ConverterMuseData,
  music21.converter.subConverters.ConverterMusicXML,
  music21.converter.subConverters.ConverterNoteworthy,
  music21.converter.subConverters.ConverterNoteworthyBinary,
  music21.converter.subConverters.ConverterRomanText,
  music21.converter.subConverters.ConverterScala,
  music21.converter.subConverters.ConverterTinyNotation]

And the formats that it can write:

converter.Converter().subconvertersList('output')
 [music21.converter.subConverters.ConverterBraille,
  music21.converter.subConverters.ConverterLilypond,
  music21.converter.subConverters.ConverterMidi,
  music21.converter.subConverters.ConverterMusicXML,
  music21.converter.subConverters.ConverterScala,
  music21.converter.subConverters.ConverterText,
  music21.converter.subConverters.ConverterTextLine,
  music21.converter.subConverters.ConverterVexflow]

To output a file, either call .show("format") on the stream (where format can be musicxml, braille, midi, etc.) or to keep the file on disk, use .write("format", "filename").

Some of the available formats will be listed below; the most important ones for now are the output formats (since music21 will figure out inputs automatically). They are braille, lilypond, midi, musicxml, scala, text, and vexflow.

Some formats have sub-formats, for instance both musicxml and lilypond have a .png subformat which converts directly to a .png file. To use that, call .show("musicxml.png").

Some formats have abbreviations also, so musicxml is also xml, lilypond is lily, and (for ease of typing), text is t.

Getting and working with MusicXML Files

Numerous MusicXML files can be found at the following URLs.

MusicXML files sometimes have the extension .xml and sometimes .mxl. Usually the latter are compressed music XML files; they load just the same.

The format for musicxml, is, of course, musicxml.

Getting and working with Humdrum Files

Humdrum is a file format developed by David Huron at Ohio State University which is great at encoding works for computational analysis. The Humdrum format includes many subformats (“spine classes”) of which music21 supports the general class, the kern format, and the dynam dynamics format.

Parsing Humdrum files is exactly as parsing other data formats. Simply call the music21.converter.parse() function on the desired file path or URL.

sBach = converter.parse('http://kern.ccarh.org/cgi-bin/ksdata?' +
                        'l=users/craig/classical/bach/cello&file=bwv1007-01.krn&f=kern')

Over one hundred thousand Kern files can be found at the following URL.

http://kern.humdrum.org/

Getting and working with ABC Files

ABC is a text-based format that can encode lots of musical types, but is especially great for monophonic songs, such as folk songs. If you’re in the folk song world, you’ll love working with ABC.

Parsing ABC files is exactly as parsing other data formats. Simply call the music21.converter.parse() function on the desired file path or URL.

o = converter.parse('/Users/cuthbert/Documents/Music21/praludium.abc')

Large collections of ABC are available from numerous on-line repositories. The following links are just a few of the many resources available.

http://abcnotation.com

http://www.serpentpublications.org

ABC Opus files

Note that many ABC files define more than one complete musical work. If an ABC file defines more than one work, an Opus object is returned. Opus objects, a Stream subclass, provide convenience methods for accessing multiple Score objects.

You can get a whole bunch of pieces together just by parsing the file. For instance, here’s an Opus:

o = corpus.parse('josquin/ovenusbant')
o
 <music21.stream.Opus 0x10760e358>

Reference work numbers (e.g., the “X:” metadata tag in ABC) are stored in Metadata objects in each contained Score. Access to these numbers from the Opus is available with the music21.stream.Opus.getNumbers() method. Additionally, the Score object can be directly obtained with the getScoreByNumber() method.

o = corpus.parse('josquin/ovenusbant')
o.getNumbers()
 ['1', '2', '3']
s = o.getScoreByNumber(2)
s.metadata.title
 'O Venus bant'

Direct access to Score objects contained in an Opus by title is available with the getScoreByTitle() method.

o = corpus.parse('essenFolksong/erk5')
s = o.getScoreByTitle('Vrienden, kommt alle gaere')
s
 <music21.stream.Score 0x1042ab080>
s.metadata.title
 'Vrienden, kommt alle gaere'

Some ABC files, such as those in corpus/essenFolksong have hundreds or thousands of files. The way we’ve been doing things before is to parse all of them and then select the one we want. If you know the number of the file you want, however, you can pass to converter.parse or corpus.parse a number=X attribute to get just that one. It will return a Score object

s = corpus.parse('essenFolksong/erk5', number=2)
s
 <music21.stream.Score 0x10a064128>

ABC single-part Opus files

In some cases an ABC file may define individual parts each as a separate score, sort of like a Renaissance partbook. When parsed, these parts can be combined from the Opus into a single Score with the music21.stream.Opus.mergeScores() method.

For instance, here is Josquin’s “Mille Regretz” (spelled with an s) stored as four individual parts each as its own score:

o = corpus.parse('josquin/milleRegrets')
len(o.scores)
 4
len(o.scores[0].parts)
 1
o.scores[0].measures(1, 20).show()
../_images/usersGuide_08_installingMusicXML_52_0.png

So, that’s not too helpful. We can run mergeScores to bring them into a single score with four parts.

s = o.mergeScores()
s.metadata.title
 'Mille regrets'
len(s.parts)
 4
s.measures(1, 10).show()
../_images/usersGuide_08_installingMusicXML_56_0.png

Parsing Musedata Files

Musedata is a format devised by Walter Hewlett (yes, of HP lineage) in the 1980s that is highly memory efficient. Probably not the best format for modern computers, but there’s a huge collection of Musedata files out on the net of many standard repertory pieces.

Both stage 1 (limited encoding) and stage 2 (rich encoding) Musedata file formats are supported by Music21. Multi-part Musedata (stage 2) files, zipped archives, and directories containing individual files for each part (stage 1 or stage 2) can be imported with the music21.converter.parse() function on the desired file path or URL.

Note that access restrictions prevent demonstrating Musedata conversion. Downloading or using Musedata files requires sending a written access agreement to the owners.

Parsing MIDI Files

MIDI input and output is handled in the same was other formats. Simply call the music21.converter.parse() function on the desired file path or URL.

Remember (or learn if you haven’t yet), that MIDI has no information about enharmonic spelling (C# and Db are the same), and that detecting the lengths of notes can be difficult. Music21 does very well with MIDI files that were created in notation software or sequencing software, but has a harder time handling MIDI files created by recording live input. For those files, we suggest converting the MIDI files in software such as Finale that has a more sophisticated MIDI to MusicXML conversion routine.

Conclusion

One of music21‘s core strengths is the number of different file formats it handles. Some people who don’t use music21 for anything else use it as a format converter. We’re happy about that, but think, hey, there’s a lot more that you can do with it than that. Let’s move on in the next chapter to one of the tools that music21 has for analysis that almost nothing else out there has: Chapter 9: Chordify which reduces scores to chordal collections.