Example of Python initialization enabling the isolated mode::
PyConfig config = PyConfig_INIT; config.isolated = 1;
Haven't we already used extenal values by this point that should have been isolated?
On this specific example, "config.isolated = 1;" ensures that Py_PreInitialize() is also called internally with "PyPreConfig.isolated = 1".
I'd rather have the isolation up front. Or better yet, make isolation the default unless you call one of the "FromArgs" functions, and then we don't actually need the config setting at all.
While there are supporters of an "isolated Python" (sometimes called "system python"), the fact that it doesn't exist in any Linux distribution nor on any other operating system (Windows, macOS, FreeBSD), whereas it's already doable in Python 3.6 with Py_IsolatedFlag=1 makes me think that users like the ability to control Python with environment variables and configuration files. I would prefer to leave Python as not isolated by default. It's just a matter of comment line arguments.
* The PEP 432 stores ``PYTHONCASEOK`` into the config. Do we need to add something for that into ``PyConfig``? How would it be exposed at the Python level for ``importlib``? Passed as an argument to ``importlib._bootstrap._setup()`` maybe? It can be added later if needed.
Could we convert it into an xoption? It's very rarely used, to my knowledge.
The first question is if there is any need for an embedder to change this option. Currently, importlib._bootstrap_external._install() reads the environment variable and it's the only way to control the option. ... By the way, importlib reads PYTHONCASEOK environment varaible even if isolated mode is enabled (sys.flags.isolated is equal to 1). Is it a bug? :-) Victor