The idea about "checked exceptions" appeared several times in various places. I used to think that this would be hard to support for any realistic use cases. But now I think there may be a chance

to turn this into a usable feature if one frames it correctly (e.g. the focus could be on user defined exceptions, rather than on standard ones, since there is no way we can annotate every function in typeshed).

But this is probably not the best place to the start the discussion (we may come back here if we will have a proposal). I would recommend to post either on typing GitHub tracker, or mypy GitHub tracker,

or on typing SIG mailing list.

IMO the part about side effects is a non-starter.

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Ivan