Hi @rth, this is great news, thanks for the initial work on this!

I hope you'll get the emscripten update fightened during the sprint. I'll take a look at the minor problems in a few days. What do you think about making a separate branch for python38 to merge further pull requests, especially for package contributions? We then might first concentrate on Pyodides core to run with Python 3.8 and then partially extend to the packages.

What do you think about making a separate branch for python38 to merge further pull requests, especially for package contributions?

I think this PR is not that far from being mergable. There are just 8 failing test modules in the CPython test suite (though I also still need to update the list of CPython tests). The rest of the packages appear to build fine (aside from cytoolz which I updated). Generally packages that worked with Python 3.7 will likely also work with 3.8 aside for some warnings. We can update packages and likely emscripten warning in a follow up PR.

Don't hesitate to either push fixes directly to this branch (you should have access being a maintainer) or open PRs to this branch on my fork. I'll also try to look into failing tests this week.

I think CPython tests should now pass. I have skipped a few using the async module or subprocess, and patched others.

The only blocker IMO is the test_open_url failure (and of other tests that use pyodide.open_url) both in Chrome and Firefox with,

selenium.common.exceptions.WebDriverException: Message: xpath lookup error: Failed to execute 'send' on 'XMLHttpRequest': Failed to load 'http://127.0.0.1:39271/test/data.txt'.
E         (Session info: headless chrome=83.0.4103.116)
E         (Driver info: chromedriver=2.41.578700 (2f1ed5f9343c13f73144538f15c00b370eda6706),platform=Linux 5.4.0-39-generic x86_64)

/usr/local/lib/python3.8/site-packages/selenium/webdriver/remote/errorhandler.py:242: WebDriverException
------------------------------------------------------ Captured stdout teardown -------------------------------------------------------
Error: Failed to execute 'send' on 'XMLHttpRequest': Failed to load 'http://127.0.0.1:39271/test/data.txt'.
    at _hiwire_call_member (http://127.0.0.1:39271/pyodide.asm.js:8:31734)
    at _JsBoundMethod_Call (http://127.0.0.1:39271/pyodide.asm.wasm:wasm-function[339]:0xfeb44)
    at http://127.0.0.1:39271/pyodide.asm.wasm:wasm-function[15117]:0x9ade0a
    at __PyObject_MakeTpCall (http://127.0.0.1:39271/pyodide.asm.wasm:wasm-function[828]:0x134900)
    at _call_function (http://127.0.0.1:39271/pyodide.asm.wasm:wasm-function[2832]:0x342b3d)
    at __PyEval_EvalFrameDefault (http://127.0.0.1:39271/pyodide.asm.wasm:wasm-function[2825]:0x33b99a)
    at http://127.0.0.1:39271/pyodide.asm.wasm:wasm-function[20875]:0x9c1c2e

which seems to indicate that something in hiwire is not working as it should and might need updating for Python 3.8

Edit: probably need to read through https://docs.python.org/3.8/whatsnew/3.8.html#changes-in-the-c-api in mode detail.

Edit2: actually it was an issue with the test server.

@phorward This should now be ready for a review. The one lxml failure on chrome which happens from time to time is a known unrelated issue (#544 (comment)) everything else passes.

If you merge, don't forget to use the "Squash and Merge" UI button :)