gh-127873: Only check sys.flags.ignore_environment for PYTHON* env vars

[hugovk]

When -E is passed (and therefore sys.flags.ignore_environment is true), we should only ignore only env vars matching PYTHON*; in this case, only PYTHON_COLORS.

We should not ignore the other env vars: FORCE_COLOR/NO_COLOR/TERM.

Re: https://docs.python.org/3/using/cmdline.html#cmdoption-E

Fixing this revealed some tests that failed because of inserted colour codes. For example, in "ZeroDivisionError: division by zero", the parts "ZeroDivisionError", ":" and "division by zero" are all different colours.

For these test cases, I wrapped them with the @force_not_colorized decorator, or, where there were a number of them, I wrapped the test class in the new force_not_colorized_test_class decorator. This was a suggestion from #127223 (comment). And from that PR, I replaced some of the numerous function decorators with the class decorator.

• Issue: can_colorize() ignores FORCE_COLOR/NO_COLOR/TERM when -E is set #127873

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @hugovk for commit 80422ff 🤖

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[hugovk]

@pablogsal Please could you have a look at this? Thanks!

[serhiy-storchaka]

Why do we use names without the PYTHON prefix? Are FORCE_COLOR and NO_COLOR the part of some (de-facto?) standard?

[hugovk]

Why do we use names without the PYTHON prefix? Are FORCE_COLOR and NO_COLOR the part of some (de-facto?) standard?

Yes, see https://force-color.org/ and https://no-color.org.

[hugovk]

Please add tests for these environment variables when run Python with the -E option.

Updated to use make_clean_env() from the PyREPL tests (and moved it to test.support for re-use), which removes the PYTHON* env vars to isolate the tests and simulate the -E option.

[serhiy-storchaka]

LGTM. Although you can use support.force_not_colorized_test_class in few more files.

[hugovk]

Thank you for the reviews!

[miss-islington-app]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @hugovk, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 05d12eecbde1ace39826320cadf8e673d709b229 3.13 

[bedevere-app]

GH-129138 is a backport of this pull request to the 3.13 branch.