Supporting Python 3.9

[hauntsaninja]

The next release needs to support Python 3.9

Here's my checklist of what's left:

• PEP 585 support (mostly implement PEP 585 Generic Builtins (Partially solves #7907) #9564)
• PEP 614 testing (Add test for PEP 614 #9759)
• Merge and test new build process for 3.9 wheels (misc: update wheel building and release scripts #9570, mypy_mypyc-wheels: rewrite using Github Actions and cibuildwheel mypyc/mypy_mypyc-wheels#11)
• Add 3.9 to trove classifiers (Add Python 3.9 to trove classifiers #9887)
• Improved documentation of PEP 563 + PEP 585 (Document PEP 585, 563, 604 and more. #9763)
• mypy_extensions support for 3.9 (Add 3.9 to the list of classifiers mypy_extensions#20 / Make a release that supports Python 3.9 mypy_extensions#21)

To clarify the state of support for users stumbling upon this issue, mypy 0.790 will mostly work with Python 3.9.
There are two caveats to running mypy with 3.9:

1. you won't be able to use list[int] syntax without mypy complaining,
2. mypy will be slower since we haven't released mypyc compiled wheels for 3.9.

Note that typeshed in 0.790 has pretty good support for Python 3.9, so using new stdlib functionality should work fine.

PS: if you're getting error: syntax error in type comment with Python 3.9, it's because you're using a really old mypy and you should upgrade to a recent release.

[intgr]

The next release needs to support Python 3.9

I wouldn't make all of these hard requirements. I'd very much like to see a mypy release with binary wheels for 3.9 even before all of these items are addressed.

[gvanrossum]

Well, we still have the 0.790 release branch so we could just create wheels for that and push those. (Or make whatever tweak are necessary on that branch and push 0.791.)

[hauntsaninja]

@intgr Agreed that I wouldn't block an otherwise scheduled release on this, but there isn't currently a scheduled release / at this point the checklist^ isn't much additional effort to complete.

If someone with the ability to release is interested in adding 3.9 wheels to 0.790, you'll need to cherry pick #9552 and #9562 (and merge the aforementioned mypyc wheel repo change). Note mypyc is broken in the 0.790 sdist so you should cherry pick #9587 as well (see #9290 (comment)).

[gvanrossum]

Here's hoping someone wants to take a stab!

[JukkaL]

We hopefully have a full release soonish, but again there are a lot of issues to address with Dropbox internal repos (previously these have mostly been typeshed issues). Otherwise there are no blockers for a new release.

I haven't had a lot of time to dedicate to mypy in the past weeks but I'm trying to carve out more time for it before the end of the year.

[bsolomon1124]

Mypy looks to be chugging along okay on 3.9 but (as expected, I understand this support has not been implemented yet) throws a bunch of error: "<xxx>" is not subscriptable. Related to #7239, is there a way to blanket-silence all [misc] error codes in mypy.ini? (Even better would be the ability to silence by a pattern, such as is not subscriptable.)

Edit: have resorted to

set -o pipefail && python3 -m mypy | grep --color=always -E -v '(tuple|dict|list|set)" is not subscriptable'

though this will return a false-positive exit code if the false-positive on type-hinting generics is the only discovered issue.

[cdce8p]

@bsolomon1124 I don't know if that's of any help, but you could try installing the latest mypy commit with:

pip install -U git+git://github.com/python/mypy.git@master  # or replace `master` with commit hash

The is not subscriptable error was fixed with #9564, so this might be a temporary fix until the next version is released.

[hauntsaninja]

Just to follow up, if people want 3.9 wheels from latest master, they're now available at https://github.com/mypyc/mypy_mypyc-wheels/releases/latest

[gvanrossum]

Can we get 3.10 wheels? :-)-- --Guido (mobile)

[hauntsaninja]

Not easily right now. We'd need 3.10 support in https://github.com/pypa/manylinux and https://github.com/joerick/cibuildwheel. But once that happens, it should be a two-liner.

[hauntsaninja]

mypy 0.800 has been released and includes all of^

[Hultner]

mypy 0.800 has been released and includes all of^

Woho! Looking forward to try it out!

[wbadart]

Hey all- cross-posting my comment from #9564 in case anyone else has had issues with PEP 585 in type aliases on 0.800: #9564 (comment)