[GitHub] [beam] tvalentyn commented on issue #22969: Discrepancy in behavior of `DoFn.process()` when `yield` is combined with `return` statement, or vice versa

["tvalentyn (via GitHub)" <gi...@apache.org>]

tvalentyn commented on issue #22969:
URL: https://github.com/apache/beam/issues/22969#issuecomment-1462730124

   Taking a closer look, the unexpected behavior is not caused by Beam but rather how Python interprets a function with `yield` and `return` statements mixed together. See: https://stackoverflow.com/questions/16780002/return-in-generator-together-with-yield which summarizes it.
   
   For example:
   
   ```
   def foo(c):
     if (c):
       yield "foo"
     else:
       return "bar
   ```
   
   ```
   list(foo(True))
   Out: ['foo']
   ```
   
   ```
   list(foo(False))
   Out: []
   ```
   
   ```next(foo(False))``` raises StopIteration: bar
   
   Seems that such mix-and-match was an error in Python 2.


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