python version checks don't seem to work with 0.780 #8990

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1. srittau commented on Jun 11, 2020

   

   srittau

   on Jun 11, 2020

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   This is a typeshed issue. ForwardRef is only defined for Python 3.7+, since it was added then under that name. The previous _ForwardRef name is not represented. PR for typeshed welcome that adds it.
2. samuelcolvin commented on Jun 11, 2020

   

   samuelcolvin

   on Jun 11, 2020

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   okay, but is there any way around this using # type: ignore for both python 3.6 and 3.7?

   I don't understand why the errors are different between python versions.

   There seems no way to specify a "type ignore" that only applies to one python version.

   Linked PR on pydantic pydantic/pydantic#1598
3. hauntsaninja commented on Jun 11, 2020

   

   hauntsaninja

   on Jun 11, 2020

   Last edited by hauntsaninja

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   Basically a dupe of #8823 (typeshed-specific details aside)

   You should be able to work around with something like:

   from typing import Any, TYPE_CHECKING
   
   if TYPE_CHECKING:
       ForwardRef: Any
   else:
       from typing import ...
   

   which isn't ideal, since mypy will now treat ForwardRef as Any.

   Edit: Actually, you could do the following:

   ~/tmp λ cat test1.py                      
   import sys
   if sys.version_info >= (3, 7):
       from typing import ForwardRef
   else:
       import typing
       from typing import cast, Any
       ForwardRef = cast(Any, typing)._ForwardRef
   
   reveal_type(ForwardRef)
   ~/tmp λ mypy --python-version 3.8 test1.py
   test1.py:9: note: Revealed type is 'def (arg: builtins.str, is_argument: builtins.bool =) -> typing.ForwardRef'
   ~/tmp λ mypy --python-version 3.6 test1.py
   test1.py:9: note: Revealed type is 'Any'
   
4. ilevkivskyi commented on Jun 12, 2020

   

   ilevkivskyi

   on Jun 12, 2020

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   It doesn't look like there is a (new) action item for mypy here, so closing.
5. ilevkivskyi

   closed this as completedon Jun 12, 2020
6. samuelcolvin commented on Jun 25, 2020

   

   samuelcolvin

   on Jun 25, 2020

   Last edited by samuelcolvin

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   @hauntsaninja thanks for pointing to the other issue. Unfortunately you ForwardRef = cast(Any, typing)._ForwardRef solution doesn't work - this is currently preventing pydantic from upgrading latest mypy (I've found another work around).