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Posted to github@beam.apache.org by GitBox <gi...@apache.org> on 2022/06/03 20:15:15 UTC

[GitHub] [beam] kennknowles opened a new issue, #18712: DoFn.process should raise exception if something other than a List is returned

kennknowles opened a new issue, #18712:
URL: https://github.com/apache/beam/issues/18712

   The process method of DoFns can either return values or yield values. In the case of returning values, it expects a List of elements to be returned. When returning a single value, it is easy to forget this, and return the value instead.
   
   Correct way:
   
   `class SomeDoFn(beam.DoFn)`
    `  def process(self, elem):`
    `    return ['a']`
   
   Incorrect way:
   
   `class SomeDoFn(beam.DoFn)`
    `  def process(self, elem):`
    `    return 'a'`
   
   A pipeline with the incorrect DoFn will fail will a cryptic error message without a direct indication that the actual error is due to SomeDoFn returning an element instead of a List containing that element. This issue is very time-consuming to track down.
   
   It would be good if the pipeline could raise an exception or otherwise indicate that the DoFn is incorrectly returning an element instead of a List to make it easier to identify the error.
   
   Imported from Jira [BEAM-3530](https://issues.apache.org/jira/browse/BEAM-3530). Original Jira may contain additional context.
   Reported by: chuanyu.


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[GitHub] [beam] toransahu commented on issue #18712: DoFn.process should raise exception if something other than a List is returned

Posted by GitBox <gi...@apache.org>.
toransahu commented on issue #18712:
URL: https://github.com/apache/beam/issues/18712#issuecomment-1232859822

   FYI, other behavioral issue observed with `DoFn.process` is : https://github.com/apache/beam/issues/22969


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[GitHub] [beam] kennknowles commented on issue #18712: DoFn.process should raise exception if something other than a List is returned

Posted by GitBox <gi...@apache.org>.
kennknowles commented on issue #18712:
URL: https://github.com/apache/beam/issues/18712#issuecomment-1272124476

   @tvalentyn @robertwb do type hints not catch this?


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