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https://issues.apache.org/jira/browse/BEAM-12920?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Valentyn Tymofieiev reassigned BEAM-12920:
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Assignee: Valentyn Tymofieiev
> Convert To Bare Types Fails on Generators in Python 3.9
> -------------------------------------------------------
>
> Key: BEAM-12920
> URL: https://issues.apache.org/jira/browse/BEAM-12920
> Project: Beam
> Issue Type: Sub-task
> Components: sdk-py-core
> Affects Versions: 2.32.0
> Environment: Python 3.9.7
> Linux Mint 20.2, Kernel: 5.4.0-84-generic
> Reporter: Jonathan Hourany
> Assignee: Valentyn Tymofieiev
> Priority: P2
> Fix For: Not applicable
>
>
> In Python 3.9 the test
> [test_convert_bare_types|https://github.com/apache/beam/blob/6c1c19d6c711babf5f5f042fa465be20948caff6/sdks/python/apache_beam/typehints/native_type_compatibility.py#L40]
> fails when testing the following Generator test case
> {code:python}
> test_cases += [
> (
> 'bare generator',
> typing.Generator,
> typehints.Generator[typehints.TypeVariable('T_co')]),
> ]
> {code}
> Raising the following {{ValueError}}
> {noformat}
> ./sdks/python/apache_beam/typehints/native_type_compatibility_test.py::NativeTypeCompatibilityTest::test_convert_bare_types
> Failed: [undefined]ValueError: Unsupported Generator with no arguments.
> {noformat}
> ----
> The immediate cause may be stemming from
> [_get_args|https://github.com/apache/beam/blob/6c1c19d6c711babf5f5f042fa465be20948caff6/sdks/python/apache_beam/typehints/native_type_compatibility.py#L40]
> which attempts to access a type's ___args___ attribute. In Python 3.9 bare
> generators no longer instantiate with a default ___args___ attribute. Only
> when instantiated with args do they get one (see example below).
> However, despite it's name the test doesn't create a generator that's
> totally bare, so the deeper cause may be coming from the way
> {{typinghints.Generator}} is constructed.
> h3. Examples
> {code:python}
> # Python 3.7.5
> In [1]: from typing import Generator
> In [2]: Generator.__args__
> Out[2]: (+T_co, -T_contra, +V_co)
> {code}
> ----
> {code:python}
> # Python 3.9.7
> In [1]: from typing import Generator
> In [2]: Generator.__args__
> ---------------------------------------------------------------------------
> AttributeError Traceback (most recent call last)
> <ipython-input-2-3e272b948083> in <module>
> ----> 1 Generator.__args__
> ~/.pyenv/versions/3.9.7/lib/python3.9/typing.py in __getattr__(self, attr)
> 704 if '__origin__' in self.__dict__ and not _is_dunder(attr):
> 705 return getattr(self.__origin__, attr)
> --> 706 raise AttributeError(attr)
> 707
> 708 def __setattr__(self, attr, val):
> AttributeError: __args__
> In [3]: # Initializing with args, however, creates the needed attr
> In [4]: Generator[int, int, int].__args__
> Out[4]: (int, int, int)
> {code}
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