Tuesday, September 1, 2020

Music21 v6 Released!

Music21 v6 is OUT as v6.1.0! This represents over 500 commits over the past 14 months since v5.7 was released.

Many thanks to Jacob Tyler Walls (JTW below) who made so many contributions to the v6 branch, both big and small. Mad props and round of applause!

v6 fully supports Python 3.8 and removes support for Python 3.5. v6 will be the last major release to support Python 3.6 and we will work on Python 3.9 support immediately.

As with all new v.X releases of music21 there are improvements and some backwards incompatible changes (not too many)

In no particular order, here are the things to look for in the new music21 v6:

  • Type hints throughout music21 -- when you program with a sophisticated IDE you will be able to see what is returned and required as attributes in much of music21.

  • music21 is no longer packaged with external modules; these will be installed when installing music21 via pip (otherwise run pip install -r requirements.txt). Speed and security improvements come with this.

  • converter.parse('file.mid', quantizePost=False) will let you load in a MIDI file without any quantizing. (Thanks JTW)

  • Lots more values cached = faster music21; RomanNumerals in particular are over an order of magnitude faster, and Chords are faster too. If you ever have a problem, all Music21Objects have a .clearCache() function. Just add @cacheMethod as a decorator to a method and it will use the caching routine.

  • Intervals have been rewritten to use properties entirely. So whatever happens to an Interval, its semiSimpleNiceName (to take one of dozens of examples) will always be up to date. Intervals use Specifiers that are enums like interval. Specifier.PERFECTinstead of inscrutable numbers. (those inscrutable numbers still work though) Specifiers are more than just standard enums -- they can invert themselves, do semitonesAboveMajor() etc. Interval geeks rejoice.

  • Intervals given a noteStart and a name will generate noteEnd automagically. They also get transposePitch() improvements along the way.

  • KeySignature gets transposePitchFromC() which takes a pitch in C major and returns the pitch in the same scale degree in this key..

  • Voices with gaps in them work way better in MusicXML. Repeat endings with multiple numbers like 1,2 r/t with musicxml (JTW)

  • TSV files which encode harmonic analysis can now be parsed (Thanks Mark Gotham)

  • Humdrum harm spines parse now, giving another way of encoding harmonic analysis. (Thanks Néstor Nápoles López)

  • MIDI refactor: easier to subclass and extend and with many docs -- keeps a clear distinction between strings and bytes. MIDI values are all Enum classes (but IntEnums so they compare well with pure numbers)

  • StripTies works much better thanks to JTW -- and does not filter out non-Notes anymore (technically an incompatibility, but really a bug fix). Voices, etc. don't faze .stripTies() any more. Stream.voicesToParts() also preserves more elements. Chords with some notes tied and some don't no longer get merged. Note that stripTies retainContainers defaults to True now, because getting the opposite behavior is as easy as a .flat

  • Internal but important: lots of parts of music21 code that used abbreviations now spell out the whole word. This is important for our friends using screen readers. While music21 will (for historical/compatibility reasons) still use camelCase for all method names, attribute names, etc., internal variables may now use underscore_case which helps with screen readers.

  • Stream().write('mxl') will write compressed musicxml (JTW). Or write('...', format='musicxml', compress=True)

  • Improvements to VoiceLeadingQuartets (thanks Ryaan Ahmed), including finding parallel intervals with octave displacement. voiceCrossing and voiceOverlap detection.

  • Substantial improvements to RomanText: see https://dmitri.mycpanel.princeton.edu/romantext.pdf

  • RomanNumerals can specify how they represent ^6 and ^7 in minor with sixthMinor and seventhMinor keywords)

  • OMR fixers can recognize Turns and other ornaments. More merging here to come. Thanks Janelle Sands!

  • Substantial improvements to beaming routines and tests (thanks Almog Cohen!)

  • Keys now have .deriveByDegree() like Scales, so "What minor key has scale degree 3 as B-flat?" can easily be answered.

  • Improvements to dotted tuplets (Almog Cohen)

  • Chord.name/fullName now gives better names for common chords like Major/Minor triads -- no longer relies entirely on chord.tables. But even there many improvements and spelling corrections.

  • Chords expose .notes to get at the notes that make up a chord, in a different way than Chord[0] or for n in Chord -- I'm still an old Perl guy, sometimes There's More Than One Way to Do It, and this way makes some things conceptually much easier and faster.

  • More Bach Chorale fixes from Doctor Schmidt (thanks!)

  • Stream.replace(recurse=True) finally works!

  • StringIndication, FretIndication work in musicxml (thanks Peter Mitrano)

  • For those who are adventurous -- intervalNetworks are now exposed on scales.

  • prebase.ProtoM21Object -- an idea ported back from music21j: nearly every object in music21, including all Music21Objects, inherits from this super-lightweight base class which allows for querying classes and giving consistent representations. It makes working in music21 a lot more fun.

Incompatible Changes

  • Stream filters now return a new StreamIterator. So old code like:
s = stream.Stream()
sIter = s.iter

should now be written as:

s = stream.Stream()
sIter = s.iter
sIter2 = sIter.getElementsByClass('Chord')

For most people using filters within a for-loop, nothing will appear to have changed.

  • if element in stream now only returns True if the element is actually in the Stream, not if element is equal to something in the Stream. This is not normal Python behavior for __contains__ but it is something music21 users have counted on for a decade, and now it is assured.

  • MIDI has been completely refactored, so if you are mucking with MIDI internals, it's going to be completely different. If you're just using converter.parse and .write('midi') it won't have changed much.


  • Setting a pitch's accidental to a number is deprecated and to be removed soon. use b = pitch.Pitch('B4'); b.accidental = pitch.Accidental(-1).
  • some long deprecated functions removed, such as Stream.restoreActiveSites, Stream. _yieldReverseUpwardsSearch, common.standardDeviation (use statistics.stdev instead).
  • Chord sort methods no longer return the chord itself if inPlace=True
  • interval.convertSemitoneToSpecifierGenericMicrotone, convertSemitoneToSpecifierGeneric now return a Specifier Enum as their first value
  • Spelling corrections that are technically incompatible: Interval.perfectable replaces typo Interval.prefectable. Appoggiatura is spelled correctly with two-gs everywhere it's used (JTW)
  • stripTies(retainContainers=True) is now the default.
  • Half-diminished chords have ø7 etc. as their default representation.
  • MIDI.intsToHexString has become MIDI.intsToHexBytes which does what is says it does.

Small Changes/Bugs squashed:

  • A malformed spanner in musicxml will no longer crash parsing.
  • Tuplets are equal if their durations are equal. Better docs for duration equality.
  • contextSitesnextprevious, and getContextByClass have a priorityTargetOnly or activeSiteOnly keyword for searching activeSite only. Speed!
  • From music21.X import * works much more reliably.
  • Bugs fixed in feature extraction of keys.
  • serial allows "P" or "T" to be used for transpositions
  • Tone-Rows give their row in the repr.
  • Historical tone-rows no longer have Row in their name. For instance: serial.getHistoricalRowByName('SchoenbergOp37').matrix() -- the old form still works though.
  • Feature extraction on empty streams (or ones that don't have instruments or something else) works properly (JTW)
  • Feature output formats can set .ext directly, in case you need a different extension.
  • viio7 can be specified as vii07
  • Interval: reverse=True works properly
  • subprocess.run is used instead of os.system for PNG generation. Thanks Uğur Güney. Fixes using musescore with music21 in Jupyter when spaces appear in filenames. (also thanks to Frank Zalkow)
  • Better representation for many objects
  • Error handling for incorrect chord abbreviation is improved. Thanks Vikram Natarajan
  • Librettists and lyricists can be searched in metadata.  .age() works properly for living composers.
  • MIDI plays back properly in Jupyter again BUT also does not add a delay when writing out a file.
  • Voice numbers in generated musicxml are now low numbers
  • pitch.Accidental gets . setAttributeIndependently() in case you want something to look like a flat but only alter 0.8 semitones. (This appeared in v.5 at some point but was never announced)
  • Note gets a pitchChanged() method which is called by its attached pitch anytime it changes so that caches can be used. Pitch gets an informClient() method which is called anytime the pitch itself changes. There is something similar in Chords too. This squashes a lot of bugs where pitches were changing but notes/chords/scales/etc. did not act like they had changed.
  • makeAccidentals works properly in Voices (JTW)
  • MIDI parsing gets more instrument objects from more places (JTW)
  • zero-length objects at the end of streams were being ignored by makeNotation (JTW)
  • Show formats: MuseScore 3.5 compatibility. (JTW). Preview is found by default on macOS Catalina/Big Sur -- still works for older OSes. No more 'is your doc > 999 pages?' bugs!
  • Some Neo-Riemannian docs weren't showing (thanks Adam Spiers)
  • Tone profiles for key analysis have been corrected. (thanks Micah Walter)
  • scaleDegreeWithAlteration on Augmented 6th chords works.
  • .musicxml is fully recognized as a suffix.
  • Improvements to analysis.windowed (thanks Sandro Luck)
  • RepeatExpander now does nothing on a score with no repeats. Before, it crashed.
  • Sousa example couldn't show before (thanks David H. Gutteridge)
  • Verticality.removeVerticalDissonances now works (also thanks to Gutteridge)
  • Z-relation for 5Z37 (5Z17) was incorrect (thanks Rodrigo Balthar Furman for spotting this)
  • Power-users who subclass Stream to be standard storage variants: Stream().coreSelfActiveSite(el) allows for subclassing what happens when an element should normally have its activeSite set to the stream.
  • Lilypond output with UTF-8 works. Grace notes no longer crash Lilypond. Now that there is a 64-bit binary Mac version of Lilypond, it will not be removed from music21.
  • RomanNumerals compare with each other. __eq__ logically defined.
  • Modest performance improvements in sorting (Thanks Alexander Morgan)
  • Documentation and test improvements and a few bugs squashed in ABC parsing.
  • f-strings used throughout music21 allowing for more detailed error messages and many bugs to be detected and removed.


  • interval.Interval.convertSpecifier() deprecated. use parseSpecifier instead.
  • Humdrum parseData() and parseFile() are deprecated. use the general converter.parse() instead.
  • .editorial.misc is deprecated, just stick whatever you want on the .editorial object itself.


As always, I want to thank MIT, the NEH, and the Seaver Institute for supporting music21 over the years along with the community of developers who use and give back to music21.

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