Support Python 3.8

[hugovk]

The Python 3.8.0 release candidate 1 came out yesterday, with the final release scheduled for 2019-10-14.

• https://discuss.python.org/t/python-3-8-0rc1-is-now-available/2421

Our next scheduled release is 2020-01-01.

Do we want to do anything to support 3.8 before that? Or wait until 2020-01-01?

We normally do have people asking for a new Pillow release quite soon after a new Python release is out (and often before, eg. #3763).

We're already testing 3.8 dev versions on Travis CI, so we do have some confidence things work. As noted in #3763, there are already Windows wheels available for 3.8.

TODO for 3.8:

• Test on 3.8.0 final
• Add 3.8 to CIs (when available)
• Add the 3.8 Trove classifier to setup.py
• Bump to (3, 9):

  Pillow/setup.py

  Lines 27 to 33 in 94a64ea

  	if sys.platform == "win32" and sys.version_info >= (3, 8):
  	warnings.warn(
  	"Pillow does not yet support Python {}.{} and does not yet provide "
  	"prebuilt Windows binaries. We do not recommend building from "
  	"source on Windows.".format(sys.version_info.major, sys.version_info.minor),
  	RuntimeWarning,
  	)

[radarhere]

Okay. So you're suggesting Pillow 6.2.1, released just after Python 3.8 is finalised early next week.

Sounds reasonable to me.

[hugovk]

Yep, or when all the pieces are in place.

[tacaswell]

We are trying to run Matplotlib CI with the pre-releases of Python (see matplotlib/matplotlib#15418) and are currently stuck on getting Pillow to compile (Matplotlib master branch now has a hard-dep on pillow as we removed our home-grown png writer).

Any pointers on how to make this work?

[hugovk]

There are unofficial builds for Windows at https://www.lfd.uci.edu/~gohlke/pythonlibs/#pillow. Download the one you need and then you should be able to pip install it, for example:

pip install Pillow‑6.2.0‑cp38‑cp38‑win_amd64.whl

[tacaswell]

I'm not sure how to do that CI though (as reverse engineering Christoph's js obfuscation seems rude).

[hugovk]

We have a pillow-depends repo especially for CI dependencies, how about doing something like that?

[radarhere]

Just as an fyi, Python 3.8 has now been released.

[hugovk]

PR to add support for 3.8 into master: #4141. Will make one into the 6.2.x branch after that's merged.

What else is needed? Do we need to wait for anything from multibuild before updating https://github.com/python-pillow/pillow-wheels?

[radarhere]

Yes, we will need https://github.com/matthew-brett/multibuild/pull/265

[radarhere]

I've created PR python-pillow/pillow-wheels#127 to add Python 3.8 to pillow-wheels.

[hugovk]

I think we're good to do the release. Shall I do this one? I can start the prep today, although may have to finish it tomorrow.

Release issue:

• Release Pillow 6.2.1 on October 21, 2019 #4152

[radarhere]

6.2.1 has now been released with support for Python 3.8.