In main, Array and Group have __setstate__ methods that directly call __init__, which isn't great (mypy complains about this). We can avoid calling __init__ by defining __reduce__ for these classes instead of __setstate__ / __getstate__.

Note that there are a lot of store classes that use __setstate__ / __getstate__ with direct calls of __init__. Clearing that up might be in scope for additional commits to this branch.

TODO:

• [ ] Add unit tests and/or doctests in docstrings
• [ ] Add docstrings and API docs for any new/modified user-facing classes and functions
• [ ] New/modified features documented in docs/tutorial.rst
• [ ] Changes documented in docs/release.rst
• [ ] GitHub Actions have all passed
• [ ] Test coverage is 100% (Codecov passes)

Codecov Report

Merging #1089 (2c6c779) into main (ece1810) will not change coverage. The diff coverage is 100.00%.

:exclamation: Current head 2c6c779 differs from pull request most recent head 364d793. Consider uploading reports for the commit 364d793 to get more accurate results

@@           Coverage Diff           @@
##             main    #1089   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          34       34           
  Lines       13846    13844    -2     
=======================================
- Hits        13839    13837    -2     
  Misses          7        7           

Impacted Files	Coverage Δ
zarr/core.py	100.00% <100.00%> (ø)
zarr/hierarchy.py	99.78% <100.00%> (-0.01%)	:arrow_down:

Things are green and reading https://docs.python.org/3/library/pickle.html#object.reduce this seems to follow sensibly, but open to other opinions.

@d-v-b: can you coordinate the entries you want for docs/release.rst for this?