pip install lxml fails on Python 3.8 prerelease builds

[Marius Gedminas]

Python 3.8 changed the C API a bit (specifically, PyCode_New() gets an extra argument to indicate the number of positional-only arguments, IIRC). This broke Cython and all packages that rely on Cython.

The Cython bug is here: https://github.com/cython/cython/issues/2938. When it's fixed, all packages using Cython that ship pre-generated C files in their PyPI release tarballs will have to re-generate them to support Python 3.8.

(When I started filing this bug I was under the mistaken impression that a fixed Cython was already published to PyPI and all that was left to do was to do the re-generation. That turns out not to be the case. I'll leave this bug as a heads up.)

[Marius Gedminas (mgedmin)]

(A double fail award goes to me for not realizing cython and lxml share maintainers so they don't need to be told about this situation! Oops.)

[Jad Chaar (jc713)]

Hey Marius, I am having this issue as well. Will it require a new lxml release? Or how can I go about fixing this on my Python 3.8 Travis CI builds?

[Marius Gedminas (mgedmin)]

A new lxml PyPI release would be best.

(You can pip install lxml directly from git as a workaround, if you pip install cython beforehand.)

[scoder (scoder)]

Let's wait until CPython 3.8 beta 1 is at least officially out.

[Marius Gedminas (mgedmin)]

CPython 3.8 beta 1 is now officially out: https://pythoninsider.blogspot.com/2019/06/python-380b1-is-now-available-for.html

[Jad Chaar (jc713)]

Now that 3.8b1 is out, think we can get a new build of lxml soon?

[Marius Gedminas (mgedmin)]

CPython 3.8 beta 2 is out now, and guess what -- it reverts the API change! Now lxml fails because it adjusted for CPython 3.8 beta 1. See https://bugs.launchpad.net/lxml/+bug/1835492