Replace an instance of IO with a protocol

[srittau]

No description provided.

[Akuli]

Can we assume that type checkers realize how bool is Union[Literal[True], Literal[False]], and therefore close_fileobj=some_bool works?

[srittau]

Can we assume that type checkers realize how bool is Union[Literal[True], Literal[False]], and therefore close_fileobj=some_bool works?

It seems that mypy still can't. Changing the last overload to bool. That's potentially unsafe (as close is missing), but I think that's a reasonable tradeoff, considering this class is not really meant to be instantiated by the user anyway.

[Akuli]

I don't think this works as intended. If fileobj is a _ZipStream but not a _ClosableZipStream, and you pass close_fileobj=True, it will match this overload instead of erroring.

[srittau]

See above: I think this is a reasonable tradeoff, considering our "prefer false negatives over false positives" policy.

[Akuli]

Then we might as well get rid of _ClosableZipStream altogether, because distinguishing between closable and non-closable zip streams doesn't affect whether the code type-checks.

[srittau]

But having it separate has the advantage that the following fails:

ZipExtFile(my_non_closable_stream, close_fileobj=True)

The only thing that can't be checked properly is the following:

close: bool = True
ZipExtFile(my_non_closable_stream, close_fileobj=close)

[Akuli]

I don't think that fails. It doesn't match the first two overloads, but it does match the third overload which just requires any stream, and bool for close_fileobj. (Note that True converts to bool.)

[srittau]

Good point. At this point I think that maybe the first solution was the best, and until python/mypy#6113 is fixed, people just use # type: ignore?

[Akuli]

Since we prefer false negatives, it might be better to just never require a .close() method.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[Akuli]

So now there is an unnecessary class _ClosableZipStream on master?

[srittau]

I opened #5504 to improve this situation.