Changes CoGroupByKey typehint from List to Iterable

[ryanthompson591]

Changes CoGroupByKey to output an Iterable instead of a List.

This will be a breaking change and I put together a document to describe it.

The documentation of CoGroupByKey is very specific that it returns iterable and not a lists.

fixes #21556

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[ryanthompson591]

R: tvalentyn

I want to talk about this before I submit. The coGroupByKey implementation specifically does make a dictionary with a Key to list pairing.

However, the documentation is very explicit that users should expect an iterable.

I want to double check one last time we are not making a breaking change unless we have to.

[codecov[bot]]

Codecov Report

Merging #22984 (4420e58) into master (ebacef9) will decrease coverage by 0.08%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #22984      +/-   ##
==========================================
- Coverage   73.58%   73.50%   -0.09%     
==========================================
  Files         716      718       +2     
  Lines       95311    95438     +127     
==========================================
+ Hits        70138    70148      +10     
- Misses      23877    23989     +112     
- Partials     1296     1301       +5     

Flag	Coverage Δ
python	83.18% <ø> (-0.23%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
sdks/python/apache_beam/transforms/util.py	96.06% <ø> (ø)
sdks/go/pkg/beam/io/databaseio/writer.go	0.00% <0.00%> (-31.43%)	:arrow_down:
sdks/go/pkg/beam/core/state/state.go	80.85% <0.00%> (-2.75%)	:arrow_down:
...s/python/apache_beam/io/gcp/bigquery_file_loads.py	87.24% <0.00%> (-0.47%)	:arrow_down:
...hon/apache_beam/runners/worker/bundle_processor.py	93.42% <0.00%> (-0.13%)	:arrow_down:
...thon/apache_beam/ml/inference/sklearn_inference.py	95.45% <0.00%> (-0.07%)	:arrow_down:
sdks/go/pkg/beam/util/gcsx/gcs.go	27.41% <0.00%> (ø)
sdks/go/pkg/beam/artifact/stage.go	61.87% <0.00%> (ø)
sdks/go/pkg/beam/io/filesystem/util.go	96.29% <0.00%> (ø)
sdks/go/pkg/beam/io/databaseio/database.go	24.24% <0.00%> (ø)
... and 14 more

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[TheNeuralBit]

R: @tvalentyn CC: @robertwb

[TheNeuralBit]

@ryanthompson591 I can't comment on your doc so I'll mention here - it encourages users to materialize the iterable result to a list, which can lead to OOMs. I think it's ok to mention casting to a list as a last resort, but the doc should also encourage users to iterate over the iterable without materializing it if at all possible.

[TheNeuralBit]

Run Python PreCommit

[ryanthompson591]

@TheNeuralBit Thanks I'll update the doc to reflect that, discouraging changing the iterable to a list.

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[ryanthompson591]

Fixes issue https://github.com/apache/beam/issues/21556

[damccorm]

Fixes issue #21556

I think for this to take effect it has to be in the PR description (which you can edit to include it) - https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword

[ryanthompson591]

@lukecwik I updated the CHANGES.md file. I think that since the 2.42 release is cut, it is now a good time to add this change.

[ryanthompson591]

Run Python 3.9 PostCommit

[ryanthompson591]

Thanks for the comments, I think I address the major concerns and added some new sample code.

Feel free to request edit access to that doc.

[ryanthompson591]

Run Python 3.9 PostCommit

[ryanthompson591]

Run Python PreCommit

[ryanthompson591]

Run Portable_Python PreCommit

[tvalentyn]

LGTM