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Comment by codr7 | Hacker News Reader

I tried to like mypy, really did. But it always ended up in some kind of circular import tailspin for me. C++ gets around the problem by allowing separation of interface and implementation, Haskell by allowing circular imports. Maybe I missed something, maybe it's fixed by now, but that was my experience a couple of years ago.

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They made a flag TYPE_CHECKING to avoid circular import in type checking. Its ugly but works.

https://docs.python.org/3/library/typing.html#typing.TYPE_CH...

Also the circular imports was the least of the problems I’ve run into with mypy. They still can’t model a JSON type because it is recursive.

Recursive types were added in Typescript 3.7. Hopefully Python takes a page from their book.

Can you show example? I believe you can use TypedDict to express that.

It’s roughly

    JSON = Union[Dict[str, JSON], List[JSON], str, bool, int, NoneType]

TypedDict isn’t for arbitrary JSON, but it is really cool.

Ah I see, TypedDict won't be useful here.

Looks like there is a work in progress though[1] and people in the ticket provided some workarounds[2][3] for now.

[1] https://github.com/python/mypy/issues/731

[2] https://github.com/python/mypy/issues/731#issuecomment-53990...

[3] https://gist.github.com/catb0t/bd82f7815b7e95b5dd3c3ad294f3c...

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