Make `asyncio` REPL respect `python -E`

[jonathandung]

Feature or enhancement

Proposal:

To my knowledge, python -E asks the interpreter to ignore all documented environment variables starting with the PYTHON prefix that might be set. The REPL of asyncio, however, does not follow this:

1. It does not include a conditional checking sys.flags.ignore_environment, before looking at PYTHON_BASIC_REPL.
2. Executing PYTHONSTARTUP is guarded by a sys.flag.isolated check (-I) as opposed to sys.flags.ignore_environment (-E). Is this a flaw in the documentation? I think it makes sense to special-case PYTHONSTARTUP.

See the relevant portions of the code here and here, and the documentation part here.

I am making this a feature, because I am not sure if the second part is a bug or intended, in which case it is a documentation fault.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

[picnixz]

cc @ambv @pablogsal @kumaraditya303 (strictly speaking, not totally asyncio but still asyncio-related)