For the PYTHONCOERCECLOCALE=warn case, it turns out that my preferred approach to implementing bpo-34589 also naturally ends up respecting -I and -E for that (i.e. supplying -I or -E will suppressed the warning).

However, my upcoming PR for that also reinstates and expands on my original comment that explained why it was valuable to support "PYTHONCOERCECLOCALE=0 python3 -E ..." and "PYTHONCOERCECLOCALE=0 python3 -I ...": so you can readily reproduce the way that locale coercion behaves on a platform *without* a suitable target locale (e.g. CentOS 7), even if your current platform actually does have such a locale available (e.g. Fedora).