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1. JukkaL

   added

   bug

   and removed

   front end

   on Jul 17, 2014
2. ddfisher

   added

   needs discussion

   on Mar 7, 2016
3. ddfisher commented on Mar 7, 2016

   

   ddfisher

   on Mar 7, 2016

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   After we add Optional checking, maybe we can make None more consistently mean "the type containing just the value None" instead of also "the uninhabited type" and "a value you can't use".
4. gnprice

   added

   depends-on/strict-optional

   on Jul 29, 2016
5. gnprice

   added this to the This milestone has been deleted milestone on Aug 4, 2016
6. gvanrossum

   added

   priority-1-normal

   on Jan 6, 2017
7. gvanrossum

   removed this from the This milestone has been deleted milestone on Mar 29, 2017
8. ddfisher commented on Jun 28, 2017

   

   ddfisher

   on Jun 28, 2017

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   Fixed by #3024.
9. ddfisher

   closed this as completedon Jun 28, 2017
10. orenbenkiki commented on Dec 4, 2017

    

    orenbenkiki

    on Dec 4, 2017

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    In mypy version 0.501, if you write:

    from typing import List
    from typing import Optional
    from typing import Union
    from typing import Generic
    from typing import TypeVar
    
    a: List[None] = [None]
    a.append(None)
    
    b: List[Optional[None]] = [None]
    b.append(None)
    
    c: List[Union[None]] = [None]
    c.append(None)
    
    T = TypeVar('T')
    
    class Foo(Generic[T]):
        def __init__(self, value: T) -> None:
            return
    
        def append(self, value: T) -> None:
            return
    
    f: Foo[None] = Foo(None)
    f.append(None)

    Then mypy will complain:

    example.py:7: error: List item 0 has incompatible type None
    example.py:8: error: Argument 1 to "append" of "list" has incompatible type None; expected None
    example.py:10: error: List item 0 has incompatible type None
    example.py:11: error: Argument 1 to "append" of "list" has incompatible type None; expected None
    example.py:13: error: List item 0 has incompatible type None
    example.py:14: error: Argument 1 to "append" of "list" has incompatible type None; expected None
    example.py:25: error: Argument 1 to "Foo" has incompatible type None; expected None
    example.py:26: error: Argument 1 to "append" of "Foo" has incompatible type None; expected None
    

    So it seems that using None as a type still doesn't behave exactly as "the type containing just the value None" - more over, it seems like there's no way to trick mypy into declaring such a type.
11. JukkaL commented on Dec 4, 2017

    

    JukkaL

    on Dec 4, 2017

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    @orenbenkiki 0.501 is pretty old. Have you a tried the latest versions? it works for me on git master.
12. orenbenkiki commented on Dec 4, 2017

    

    orenbenkiki

    on Dec 4, 2017

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    Ah, it works in version 0.550. Thanks.

    Version 0.501 was released in March this year, if that makes it "old.".. it is great to see mypy advancing so fast!
13. JukkaL commented on Dec 4, 2017

    

    JukkaL

    on Dec 4, 2017

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    Yeah, 0.501 is already old in "mypy years" :-)
14. gvanrossum

    added

    topic-strict-optional

    on Apr 24, 2019