Bump Version

Bumping music21's version

The version lives in music21/_version.py as __version__ = 'MAJOR.MINOR.PATCHsuffix' (e.g. '11.0.0b2'). The __version_info__ tuple is derived from it automatically — only edit the string.

Two files to change, always together

1. music21/_version.py — the __version__ string.
2. music21/base.py — the single version doctest:

   >>> music21.VERSION_STR
   '11.0.0b2'
   

   This test exists specifically to force you to remember the bump. If you change _version.py without it, the doctest fails.

Verify both with:

uv run pytest --doctest-modules music21/base.py music21/_version.py

(or uv run python -c "import music21; print(music21.VERSION_STR)").

When to bump

One thing depends on the number changing: the pickled-stream cache. The version is part of the cache key, so a bump invalidates stale pickles everywhere. If nobody is holding a wrong cached parse, don't bump — the commit is the record.

• Parser or parsing-format change → always bump, even a pure refactor: someone is holding a pickle parsed by the old code. musicxml, abc, MIDI, noteworthy/NWC, humdrum, and the rest.
• Anything else → no bump: a new feature, a fix that makes code do what it already claimed, an internal refactor, a test-only or docs-only change.

"It's a bug fix" is not by itself a reason. A musicxml importer that now reads a tag it used to drop bumps, because cached parses are wrong. A scale analysis method that changed its return format does not.

A New in / Changed in marker is not a reason to bump. Those markers name a major version, at most a minor one — never a patch, never a bN beta — and moving those digits is a release decision only a human makes. Write the marker for the version the change will land in and leave _version.py alone.

Which part to change

music21 follows semver-ish rules (see the _version.py docstring for the full rationale):

• MAJOR (X) — breaks old features. Rare. A human decides this.
• MINOR (Y) — new features. Even Y = alpha/beta, odd Y = release. X.0 (e.g. 11.0) are development releases that can still change until X.1. A human decides this too; an agent changes only the patch or the beta suffix.
• PATCH (Z) — parsing/pickle-invalidating changes and other fixes that meet the bar above.
• beta suffix (bN) — successive pre-release builds of the same MAJOR.MINOR.PATCH. To cut another beta without otherwise changing the number, increment it: 11.0.0b1 → 11.0.0b2. (This is what a parser change during a …b1 cycle does.)

Changed in / New in docstring markers

Annotate a changed public interface in the affected method/class docstring. This is independent of bumping — a marker is documentation, not a version change:

• * Changed in vX: one-line explanation.
• * New in vX: one-line explanation.

Pick X from the AGENTS.md rule: if the current version is MAJOR.0…, use Changed in vMAJOR; if it's MAJOR.[even], use the next odd minor (e.g. at 10.2, write Changed in 10.3); if it's already odd, use the following odd number. (Humans remove the AI-assisted note on review; leave the version marker.)

Checklist

1. Edit __version__ in music21/_version.py.
2. Edit the VERSION_STR doctest in music21/base.py to match.
3. Add/update Changed in / New in markers on any changed public API.
4. uv run pytest --doctest-modules music21/base.py music21/_version.py.