Real argc and argv in embedded interpreter

[nordaux]

BPO	15577
Nosy	@abalkin, @vstinner, @dvarrazzo, @encukou, @ericsnowcurrently
Superseder	bpo-23427: Add sys.orig_argv: original command line arguments passed to the Python executable

^{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 2019-09-26.00:44:19.457>
created_at = <Date 2012-08-07.20:38:29.739>
labels = ['extension-modules', 'interpreter-core', 'type-feature', '3.9']
title = 'Real argc and argv in embedded interpreter'
updated_at = <Date 2020-06-08.17:25:56.658>
user = 'https://bugs.python.org/nordaux'

bugs.python.org fields:

activity = <Date 2020-06-08.17:25:56.658>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-09-26.00:44:19.457>
closer = 'vstinner'
components = ['Extension Modules', 'Interpreter Core']
creation = <Date 2012-08-07.20:38:29.739>
creator = 'nordaux'
dependencies = []
files = []
hgrepos = []
issue_num = 15577
keywords = []
message_count = 7.0
messages = ['167639', '222777', '353242', '370965', '370966', '371026', '371029']
nosy_count = 6.0
nosy_names = ['belopolsky', 'vstinner', 'piro', 'petr.viktorin', 'eric.snow', 'nordaux']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '23427'
type = 'enhancement'
url = 'https://bugs.python.org/issue15577'
versions = ['Python 3.9']

[nordaux]

I have found out certain peculiarity of interpreter in case it is embedded.
There is no way to reference to the real parameters argv, argc of main process from embedded python's C extensions.
When python is not embedded, it is task of function Py_Main, which sets the value of variables orig_argv, orig_argc.
These variables keep references to the original values of argv, argc and give opportunity to manage them from the python C extensions if necessary.
I understand that the function Py_GetArgcArgv is rarely used, and this is true, but still believe that ability to manipulate these variables should be exist in any form of python from its C extension modules.
I tried different modules of C-extensions with such functional in embedded environment, but they all causes Segmentation Fault. The problem is not only in their implementation quality without any additional inspections, but also the function Py_GetArgcArgv doesn't additionally reported that its returned, and just ruturn null pointer in self argv parameter when used in embedded environment.
The following quote all the code that refers to this functionality in Python 2.7-3.3 at the moment:

/* For Py_GetArgcArgv(); set by main() */
static char **orig_argv;
static int  orig_argc;

..........................................................................................
/* Main program */

int
Py_Main(int argc, char **argv)
{
..........................................................................................
    orig_argc = argc;           /* For Py_GetArgcArgv() */
    orig_argv = argv;
..........................................................................................
}

void
Py_GetArgcArgv(int *argc, char ***argv)
{
    *argc = orig_argc;
    *argv = orig_argv;
}

Thats why I would like to suggest something similar to such function and use it in Py_Main and probably make it available from Python C API.
And also extend Py_GetArgcArgv with more detailed null pointer handling if variables orig_argv, orig_argc had not been initialized.

void
Py_InitArgcArgv(int *argc, char ***argv)
{
    if(! *argv) return -1;

orig_argc = *argc;           /* For Py_GetArgcArgv() */
orig_argv = *argv;

    return 0;   
}

Would like to see other suggestions.
Thanks.

[BreamoreBoy]

Without a patch this issue will go nowhere. I'm assuming that this limitation must have been overcome by other projects using embedded Python. Has anybody got any ideas as to how, I certainly haven't?

[vstinner]

I only saw one request (this issue) for this feature, in 2012. So it doesn't sound really important. I close the issue.

[encukou]

FWIW, another project that needs Py_GetArgcArgv is "setproctitle": https://bugzilla.redhat.com/show_bug.cgi?id=1792059

See also: cherrypy/cherrypy#1506

[dvarrazzo]

Py_GetArgcArgv gone broke setproctitle indeed.

dvarrazzo/py-setproctitle#76

Is there a way to get the same feature in 3.9 or should setproctitle become no-op from 3.9 on and Python loses this feature?

Thank you.

[vstinner]

I mark this issue as a duplicate of bpo-23427.