PEP 432, PEP 587: Add _Py_RunMain()

[vstinner]

BPO	36471
Nosy	@ncoghlan, @vstinner
PRs	bpo-36471: Add _Py_RunMain() #12618

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-05-11.02:06:09.001>
created_at = <Date 2019-03-29.12:13:44.145>
labels = ['interpreter-core', '3.8']
title = 'PEP 432, PEP 587: Add _Py_RunMain()'
updated_at = <Date 2019-05-11.02:06:08.998>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2019-05-11.02:06:08.998>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-05-11.02:06:09.001>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2019-03-29.12:13:44.145>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 36471
keywords = ['patch']
message_count = 4.0
messages = ['339106', '339107', '339114', '342148']
nosy_count = 2.0
nosy_names = ['ncoghlan', 'vstinner']
pr_nums = ['12618']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue36471'
versions = ['Python 3.8']

[vstinner]

The PEP-587 adds new functions taking command line arguments:

Py_PreInitializeFromArgs(config, argc, argv)
Py_PreInitializeFromWideArgs(config, argc, argv)
Py_InitializeFromArgs(config, argc, argv)
Py_InitializeFromWideArgs(config, argc, argv)

I propose to add _Py_RunMain() (currently private, until PEP-587 is accepted) to be able to implement something similar to Py_Main() but with way more configuration options:

Example to create an "isolated Python" in a few line of C:
---

#include <Python.h>

int main(int argc, char *argv[])
{
    _PyCoreConfig config = _PyCoreConfig_INIT;
    config.isolated = 1;

    _PyInitError err = _Py_InitializeFromArgs(&config, argc, argv);
    if (_Py_INIT_FAILED(err)) {
        _Py_ExitInitError(err);
    }

    return _Py_RunMain();
}

---

It's like the regular "python3" program, except that it's always isolated:
---

$ my-isolated-python
Python 3.8.0a3+ (heads/run_main-dirty:d167362ecc, Mar 29 2019, 13:03:30) 
>>> 1+1
2
>>> import sys
>>> sys.flags.isolated
1

---

Using _Py_RunMain(), it becomes trivial to implement something like PEP-432's "system python" idea ;-)

[vstinner]

I'm working on a PR to implement it.

[vstinner]

New changeset 2f54908 by Victor Stinner in branch 'master':
bpo-36471: Add _Py_RunMain() (GH-12618)
2f54908

[vstinner]

The PEP-587 will decide if this function is made public or not.