[jira] [Updated] (BEAM-8519) Typehint for Python CombineFn Accumulator

["Kenneth Knowles (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/BEAM-8519?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kenneth Knowles updated BEAM-8519:
----------------------------------
    Status: Open  (was: Triage Needed)

> Typehint for Python CombineFn Accumulator
> -----------------------------------------
>
>                 Key: BEAM-8519
>                 URL: https://issues.apache.org/jira/browse/BEAM-8519
>             Project: Beam
>          Issue Type: New Feature
>          Components: sdk-py-core
>            Reporter: Yifan Mai
>            Priority: Major
>
> Feature request:
> Allow users to specify a typehint for the accumulator type of CombineFn, either through a typehints decorator, or by using Python type annotations on the CombineFn methods, or through inheriting a CombineFn [generic type|https://docs.python.org/3/library/typing.html#user-defined-generic-types].
> Benefits:
>  * Allow the user to [specify a more efficient coder|https://beam.apache.org/documentation/programming-guide/#data-encoding-and-type-safety] for accumulators if one is available. Currently users are able to do this for the input and output elements, but not the accumulators, which [always uses the fallback coder|https://github.com/apache/beam/blob/d664592ee761d45b0273edb027a18c6ed9340349/sdks/python/apache_beam/transforms/core.py#L859-L860].
>  * Allows typechecking of methods for CombineFn e.g. check that create_accumulator(), add_input() and merge_accumulators() returns accumulators. This provides better developer ergonomics as the CombineFnAPI is non-trivial.



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