[jira] [Commented] (BEAM-10979) Python CoGBK should propagate typehints

["Udi Meiri (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-10979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17208226#comment-17208226 ] 

Udi Meiri commented on BEAM-10979:
----------------------------------

My first idea would be to add annotations to CoGroupByKey.expand. From what I understand it should look like this:
{code}
  def expand(self, pcolls: Dict[T, PCollection[Tuple[K, V]]]) -> \
      PCollection[Tuple[K, Dict[T, Iterable[V]]]]:
{code}

However Beam fails to convert this to its internal typing system.
{code}
E       TypeError: Value-type parameter to a Dict hint must be a non-sequence, a type, or a TypeConstraint. apache_beam.pvalue.PCollection[typing.Tuple[~K, ~V]] is an instance of _GenericAlias.
{code}

I also believe that TypeVar binding needs special support.
Overriding default_type_hints might help here, including the infer_* and type_check_* methods.


> Python CoGBK should propagate typehints
> ---------------------------------------
>
>                 Key: BEAM-10979
>                 URL: https://issues.apache.org/jira/browse/BEAM-10979
>             Project: Beam
>          Issue Type: Improvement
>          Components: sdk-py-core
>            Reporter: Brian Hulette
>            Priority: P2
>              Labels: types
>
> Currently CoGBK erases type hints, but they could be propagated



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