Announcement: Zarr-Python version 3 release schedule

[jhamman]

This issue describes the planned development path toward the 3.0 release of Zarr-Python.

Important information

• 3.0 Roadmap and Design Doc
• 3.0 Project Board
• 3.0 Development Branch: v3 (note: as of 10/14/2024, development of has moved back to the main branch)

Release schedule

2.18.0 - May 9, 2024 (Milestone)

• Goal: prepare the way for the 3.0 releases
• Includes deprecation and/or future warnings where breaking changes are expected in 3.0
• Anticipated final minor release of 2.* series
• Additional bug fix releases may be made as needed

3.0.0.alpha0 - June 5, 2024 (Milestone)

• Goal: facilitate testing by early adopters and downstream libraries
• Includes >90% of the surface area of the expected 3.0.0 release
• May be missing some documentation, test coverage, or features beyond the core API

(edit: we are making weekly alpha releases right now)

3.0.0 - Early October, 2024 (Milestone)

• Goal: full release of Zarr-Python 3 🎉
• Includes 100% of the expected surface area of 3.0.0 release
• May or may not include extensions beyond the core v2 and v3 specs
• Minimal breaking changes relative to 2.*
• Complete migration guide

Note to contributors

Over the next 2-3 months, we expect to transition the majority of development to the v3 branch. By no means are we ceasing support for the 2.* series but the general direction of the library is toward v3. If you are considering a contribution to Zarr-Python beyond the scope of a bug fix, the v3 branch is likely your best bet.

Update 5/31/24: We have fallen off our intended timeline by a few weeks. I've updated the alpha release and full release dates accordingly.

[cwognum]

Hey @jhamman, super excited about the v3 release! 🎉

I hope you don't mind me asking, but I was wondering if you're still operating under the same timeline? Looking at the 3.0 Project Board as an outsider, it appears the team is currently behind schedule. Don't mean to critique, but we are planning to use Zarr for a project and are wondering whether it makes sense to wait for the 3.0 release.

1. Do you think you'll still release 3.0.0 by June 14th?
2. If not:
   1. Would you already be able to communicate a new date?
   2. Would you already be able to share more details about the migration process? Could Zarr archives created with v2 still be opened by v3? What about the other way around?

Thank you!

[jhamman]

Hi @cwognum - thanks for the question. We are probably a few weeks behind schedule. Hoping to get the alpha release our in the next few days. I suspect the full release will happen a few weeks behind our initial target but I don't think its worth being more specific than that at this point. I would advise you to start using Zarr-Python 2 now as the migration is going to be quite straightforward, as long as you stick to the core API.

Could Zarr archives created with v2 still be opened by v3? What about the other way around?

Yes, 100%. There are PBs of Zarr v2 data out there today and we're not expecting anyone to migrate their data.

[jakirkham]

FYI we have changed the default branch to v3 from main. So new PRs opened will automatically point to v3

The main branch is still around. Just not the default

AIUI this reflects what the current state of things has been for some time (development should be on v3 and main should be for maintenance of v2). This merely formalizes that state

[braingram]

Is there a plan for a migration guide for developers of packages that use zarr (or does one already exist)?

I maintain asdf-zarr and it looks like some API has changed including no zarr.storage zarr.creation zarr.open etc. I initially saw zarr.v2 thinking that was a compatibility API that I could use but it looks like that is being removed in #1898

[jhamman]

We have hit the first alpha release milestone! This means we will be making the 3.0.0.alpha0. Rest assured, more API compatibility changes will be coming before the full 3.0 release.

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Edit: the pre-release is now live:

• https://github.com/zarr-developers/zarr-python/releases/tag/v3.0.0-alpha
• https://pypi.org/project/zarr/3.0.0a0/