[jira] [Commented] (BEAM-4781) PTransforms that simply return their input cause portable Flink to crash.

["Maximilian Michels (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-4781?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16810719#comment-16810719 ] 

Maximilian Michels commented on BEAM-4781:
------------------------------------------

Not a Flink Runner bug. This is a bug inside the Python SDK:

{noformat}
Traceback (most recent call last):
  File "/beam-test/beam-python/src/wordcount.py", line 123, in <module>
    "--streaming",
  File "/beam-test/beam-python/src/wordcount.py", line 73, in run
    p.apply(MaybePrint())
  File "/beam-test/venv/lib/python2.7/site-packages/apache_beam/pipeline.py", line 505, in apply
    '_extract_input_pvalues' % (pvalueish, transform))
NotImplementedError: Unable to extract PValue inputs from None; either <MaybePrint(PTransform) label=[MaybePrint]> does not accept inputs of this format, or it does not properly override _extract_input_pvalues
{noformat}

> PTransforms that simply return their input cause portable Flink to crash.
> -------------------------------------------------------------------------
>
>                 Key: BEAM-4781
>                 URL: https://issues.apache.org/jira/browse/BEAM-4781
>             Project: Beam
>          Issue Type: Task
>          Components: runner-flink
>            Reporter: Robert Bradshaw
>            Assignee: Aljoscha Krettek
>            Priority: Major
>              Labels: triaged
>
> E.g.
>  
> {code:python}
> class MaybePrint(beam.PTransform):
>    def expand(self, pcoll):
>     if some_flag:
>       pcoll | beam.Map(logging.info)
>     return pcoll
> {code}
>  



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