8000 get_type_hints() always raises on forward references · Issue #508 · python/typing · GitHub
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ilevkivskyi opened this issue Dec 3, 2017 · 8 comments
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get_type_hints() always raises on forward references #508

ilevkivskyi opened this issue Dec 3, 2017 · 8 comments
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@ilevkivskyi

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@ilevkivskyi
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ericvsmith/dataclasses#92 (comment) raised an important question (this existing problem is also mentioned in PEP 563). Currently, get_type_hints will raise a NameError in situations where it might not be the desired behaviour (e.g. if used by a class decorator). For example:

def modify(cls):
    types = get_type_hints(cls)
    # do something with 'cls' and 'types'
    return cls

@modify
class C:
    linked: 'C'

It looks like it will be useful to have an option to keep forward references that are currently undefined. For example:

class C:
    x: 'ClassVar[B]'

assert get_type_hints(C, allow_forward=True) == {'x': ClassVar['B']}

class B:
    ...

assert get_type_hints(C, allow_forward=True) == {'x': ClassVar[B]}
@ilevkivskyi ilevkivskyi mentioned this issue Dec 3, 2017
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@gvanrossum
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gvanrossum commented Dec 4, 2017 via email

@ilevkivskyi ilevkivskyi self-assigned this Dec 7, 2017
@euresti euresti mentioned this issue Dec 19, 2017
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@ericvsmith ericvsmith mentioned this issue May 13, 2018
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@djrochford
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I take it this was not easy to fix? I, for one, would be very glad to see this fixed, but I gather that's unlikely to happen soon...

@ilevkivskyi
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This is not easy, but not too hard either. I just didn't have time for this, sorry.

@djrochford
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Oh, no need to apologise! I commented only in the hope of bumping this slightly higher the priority list, but I'll survive, and life is short.

@ghost
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ghost commented Jun 2, 2020

Is there any chance to get this fixed in the near future?

@ghost
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ghost commented Jun 6, 2020

You can temporarily fix this issue by passing a dict as parameter with the needed classes to the function.

@The-Compiler
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A somewhat related Python bug I've opened about this a couple of weeks ago (before finding this issue): Issue 43463: typing.get_type_hints with TYPE_CHECKING imports / getting hints for single argument - Python tracker

@antonagestam antonagestam mentioned this issue Apr 30, 2021
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@BvB93 BvB93 mentioned this issue Jun 24, 2021
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@Delgan Delgan mentioned this issue Aug 23, 2021
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@FabienArcellier FabienArcellier mentioned this issue Sep 10, 2021
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@srittau
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srittau commented Nov 4, 2021

Please report this bug to bugs.python.org if it still exists.

@srittau srittau closed this as completed Nov 4, 2021
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