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https://issues.apache.org/jira/browse/BEAM-8487?focusedWorklogId=390943&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-390943
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ASF GitHub Bot logged work on BEAM-8487:
----------------------------------------
Author: ASF GitHub Bot
Created on: 21/Feb/20 22:13
Start Date: 21/Feb/20 22:13
Worklog Time Spent: 10m
Work Description: udim commented on issue #10932: [BEAM-8487] Handle
nested forward references
URL: https://github.com/apache/beam/pull/10932#issuecomment-589859233
R: @tvalentyn
CC: @robertwb
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Issue Time Tracking
-------------------
Worklog Id: (was: 390943)
Time Spent: 1h 20m (was: 1h 10m)
> Python typehints: support forward references
> --------------------------------------------
>
> Key: BEAM-8487
> URL: https://issues.apache.org/jira/browse/BEAM-8487
> Project: Beam
> Issue Type: Bug
> Components: sdk-py-core
> Reporter: Udi Meiri
> Assignee: Udi Meiri
> Priority: Major
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> Typehints may be given as string literals:
> https://www.python.org/dev/peps/pep-0484/#forward-references
> These are currently not evaluated and result in errors.
> Example 1:
> {code}
> def test_typed_callable_string_hints(self):
> def do_fn(element: 'int') -> 'typehints.List[str]':
> return [[str(element)] * 2]
> result = [1, 2] | beam.ParDo(do_fn)
> self.assertEqual([['1', '1'], ['2', '2']], sorted(result))
> {code}
> This results in:
> {code}
> > return issubclass(sub, base)
> E TypeError: issubclass() arg 2 must be a class or tuple of classes
> typehints.py:1168: TypeError
> {code}
> Example 2:
> {code}
> def test_typed_dofn_string_hints(self):
> class MyDoFn(beam.DoFn):
> def process(self, element: 'int') -> 'typehints.List[str]':
> return [[str(element)] * 2]
> result = [1, 2] | beam.ParDo(MyDoFn())
> self.assertEqual([['1', '1'], ['2', '2']], sorted(result))
> {code}
> This results in:
> {code}
> > raise ValueError('%s is not iterable' % type_hint)
> E ValueError: typehints.List[str] is not iterable
> typehints.py:1194: ValueError
> {code}
> where the non-iterable entity the error refers to is a string literal
> ("typehints.List[str]").
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