typing: accept buffers in typing.IO.write

[JelleZijlstra]

Fixes #9082

[JelleZijlstra]

The mypy failures are a bug, python/mypy#14002.

[srittau]

This looks quite disruptive to me and I'm not sure whether it's worth it, considering the slightly legacy nature of IO.

[JelleZijlstra]

Worth noting that most of the mypy-primer fallout is due to a mypy bug (python/mypy#14002).

[hauntsaninja]

This seems useful, but given that I think I have a mypy fix, let's wait until it's released: python/mypy#14017

[AlexWaygood]

Looks like we can go back to this now, with the latest mypy release!

[AlexWaygood]

We probably don't need this type: ignore anymore (as well as several others), with the latest mypy release.

[JelleZijlstra]

Cleaned up all comments referencing that issue.

[AlexWaygood]

We do still need this type: ignore, but not because of the mypy issue linked (which is now closed) -- we need it because the definitions of writelines() in the two base classes are incompatible. The same goes for all the type: ignores in io.pyi and the one in lzma.pyi.

[JelleZijlstra]

Updated these comments.

[AlexWaygood]

These overloads might not work very well with pyright, which has different handling of self types to mypy (#9591). The same goes for the overloads on lines 401-408, and the overloads in typing.pyi. You might want to instead do something similar to what I did with re.Pattern and re.Match in #9592.

[JelleZijlstra]

Changed, and added some testcases for IO.write.

[AlexWaygood]

Ping @JelleZijlstra, have you had a chance to take a look at my review feedback? :)

[JelleZijlstra]

Oops, I think I assumed this was still blocked. I will take a look soon!

[JelleZijlstra]

hm, the new way to write the overloads makes subclassing much worse. Let me see if I can fix that.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

rich (https://github.com/Textualize/rich)
+ rich/progress.py:173: error: Definition of "writelines" in base class "IOBase" is incompatible with definition in base class "IO"  [misc]

psycopg (https://github.com/psycopg/psycopg)
+ psycopg/psycopg/copy.py:464: error: Unused "type: ignore" comment

cwltool (https://github.com/common-workflow-language/cwltool)
+ cwltool/main.py:963: error: Unused "type: ignore[arg-type]" comment

[JelleZijlstra]

Seems like we have a choice between:

1. One overload for AnyStr and another for Buffer: pyright accepts IO.write(AnyStr), but mypy hits Incorrect incompatible override report with self type + overload + TypeVar with constraints mypy#14866 and subclasses of IO classes that override the write/writelines method start complaining.
2. One overload for str and another for bytes + Buffer: mypy is fine with more subclasses, but pyright rejects IO.write(AnyStr).

I'm inclined to go with (1) because mypy's behavior is more clearly buggy than pyright's, but ideally we'd fix the mypy bug first.

[AlexWaygood]

Now that python/mypy#14882 has been merged, I guess we have two options:

• we can either merge [alt] typing: accept buffers in IO.write #9861 now (and simplify the overloads after mypy 1.2 comes out, perhaps);
• or we close [alt] typing: accept buffers in IO.write #9861, wait for mypy 1.2, and then merge this.

I'm easy either way :)