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

["Yifan Mai (Jira)" <ji...@apache.org>]

Yifan Mai created BEAM-8519:
-------------------------------

             Summary: 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


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



--
This message was sent by Atlassian Jira
(v8.3.4#803005)