(chore): export read_elem and write_elem from the main package

[ilan-gold]

To do this properly, needed to export RWAble and the sparse backed classes

• Closes Move read_elem, write_elem from experimental into main API #1158
• Tests added
• Release note added (or unnecessary)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.35%. Comparing base (a92bda8) to head (a39d178).
Report is 69 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1598      +/-   ##
==========================================
- Coverage   86.81%   84.35%   -2.46%     
==========================================
  Files          37       37              
  Lines        6005     6016      +11     
==========================================
- Hits         5213     5075     -138     
- Misses        792      941     +149     

Files with missing lines	Coverage Δ
src/anndata/__init__.py	93.54% <100.00%> (+1.54%)	⬆️
src/anndata/_core/sparse_dataset.py	92.92% <ø> (ø)
src/anndata/_types.py	87.50% <ø> (ø)
src/anndata/experimental/__init__.py	100.00% <100.00%> (ø)

... and 8 files with indirect coverage changes

[flying-sheep]

see above: define public API of CS{R,C}DataSet

[ilan-gold]

@flying-sheep I have been thinking about this a bit. Is it bad practice to keep the CS{C,R}Dataset classes experimental while exporting something from core that can deal with them? I don't think so. Even though X has the wrong type annotation, it should include CS{R,C}Dataset, and this would be an example of a public API referencing an experimental one.

[flying-sheep]

You’re right, that’s not a problem.

We could also e.g. export Protocols as CSR/CSCDataset that only expose or describe what we know we’ll keep (e.g. shape, dtype, that users can slice them via __getitem__ and convert them into arrays, …)

[flying-sheep]

why not just define def __getattr__(key: str) -> Any: ... in the experimental module directly?

https://peps.python.org/pep-0562/ exists since 3.7

[ilan-gold]

This has the advantage of never having to thinking about this again. As we move things out of experimental into the public API, we'll never have to update this.

[ilan-gold]

Maybe you could do __getattr__ without a circular import? I guess I can try but I just kind of assumed not

[ilan-gold]

Although now that I think about it, maybe a blanket warning isn't such a good idea...would want to be explicit about deprecations

[flying-sheep]

You can just import inside of __getattr__, no?

experimental/__init__.py:

[…]

def __getattr__(key: str) -> Any:
    import anndata

    if key in anndata.__all__: ...