bump-version

Development

When and how to bump music21's version number. Use this whenever a change warrants a new version — especially any change to a parsing format or parser (musicxml, abc, MIDI, noteworthy/NWC, humdrum, etc.), since those invalidate the pickled-stream cache — as well as new features and bug fixes. Covers which digit to change, the even/odd minor and beta-suffix conventions, the TWO files to edit, and the `Changed in`/`New in` docstring markers.

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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

music21/_version.py — the __version__ string.
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

Parsing-format / parser changes (most common reason). Any change to how a format is read or written — musicxml, abc, MIDI, noteworthy/NWC, humdrum, etc. — should bump the version, even a refactor, because the version is baked into the pickled-stream cache (cached parsed files). Bumping invalidates stale pickles so users don't get results from the old parser. This is the rule in AGENTS.md ("Changes to parsing formats … need to update the patch version").
New feature → bump (see digit rules below); mark it in docstrings with * New in vX: ….
Bug fix → bump the patch; if it changes public behavior, mark * Changed in vX: ….
Pure internal refactor with no behavioral/pickle impact → usually no bump.

Which part to change

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

MAJOR (X) — breaks old features. Rare.
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.
PATCH (Z) — bug fixes and parsing/pickle-invalidating changes.
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

When a bump accompanies a public-interface change, annotate the affected method/class docstring:

* 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.)