[jira] [Created] (BEAM-8487) Python typehints: support forward references

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

Udi Meiri created BEAM-8487:
-------------------------------

             Summary: 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


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]").




--
This message was sent by Atlassian Jira
(v8.3.4#803005)