Add sys.orig_argv: original command line arguments passed to the Python executable

[jgehrcke]

BPO	23427
Nosy	@birkenfeld, @pitrou, @vstinner, @jwilk, @bitdancer, @jgehrcke, @zware
PRs	bpo-23427: Add sys.orig_argv attribute #20729
Files	sys_argv_cmd.patch

^{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 2020-06-29.22:53:45.902>
created_at = <Date 2015-02-09.21:09:28.046>
labels = ['interpreter-core', 'type-feature', '3.10']
title = 'Add sys.orig_argv: original command line arguments passed to the Python executable'
updated_at = <Date 2020-06-29.22:53:45.901>
user = 'https://github.com/jgehrcke'

bugs.python.org fields:

activity = <Date 2020-06-29.22:53:45.901>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-06-29.22:53:45.902>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2015-02-09.21:09:28.046>
creator = 'jgehrcke'
dependencies = []
files = ['38065']
hgrepos = []
issue_num = 23427
keywords = ['patch']
message_count = 15.0
messages = ['235633', '235645', '235677', '235680', '235681', '235705', '371017', '371022', '371025', '371027', '371028', '371031', '372157', '372639', '372640']
nosy_count = 9.0
nosy_names = ['georg.brandl', 'pitrou', 'vstinner', 'jwilk', 'r.david.murray', 'jgehrcke', 'docs@python', 'zach.ware', 'krivushinme']
pr_nums = ['20729']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue23427'
versions = ['Python 3.10']

[jgehrcke]

When Python is invoked with the -c command switch, the command string does not get exposed in sys.argv:

    $ python -c "import sys; print(sys.argv)"
    ['-c']

    $ python -c "import sys; print(sys.argv)" arg1
    ['-c', 'arg1']

The command string does not get exposed anywhere, AFAIK, so it is inaccessible from within Python programs. There might be application scenarios in which it is useful to access the command string, such as for debugging purposes. One scenario is when a Python session should be able to "re-spawn" itself in a subprocess (I came across this question on StackOverflow: http://stackoverflow.com/q/28412903/145400)

I propose to make the command string accessible. If you agree that it might make sense, the question is *how/where* to expose it.

One possible way is to retain it in sys.argv, as in this example:

    $ python -c "import sys; print(sys.argv)" "arg1"
    ['-c', 'import sys; print(sys.argv)', 'arg1']

The current sys.argv docs say

If the command was executed using the -c command line option to
the interpreter, argv[0] is set to the string '-c'.

This sentence could then be adjusted to

"[...], argv[0] is set to the string '-c', and argv[1] contains the command."

This method breaks existing applications that are started with the -c method and that consume command line arguments in a sys.argv[1:] fashion. The tests in Lib/test/test_cmd_line.py all pass, however.

A second method would be to change sys.argv[0] from '-c' to '-c command'. This would break existing applications that check for sys.argv[0] == 'c'.

A third method would be to leave sys.argv as it is, and expose the command with a new attribute in the sys module.

I have attached a patch for variant 1 (passes all tests in Lib/test/test_cmd_line.py), to demonstrate which code is affected: the translation from the "real" argv to sys' argv is triggered in Modules/main.c. The patch does not change behavior of '-m' (it's funny, however, that the current version of main.c at first replaces the module string with '-m', whereas the runpy module later on replaces '-m' with the path to the module file anyway.).

As a side node, I figure that the sys.argv documentation should be adjusted to properly reflect the -m behavior, which is:

    $ ./python -m testmodule foo
    testmodule sys.argv: ['/data/local/pythondev/pythontip/cpython/testmodule.py', 'foo']

Let me hear your comments, and I am willing to work on code and doc patches, thanks!

[vstinner]

sys.argv must not be changed. It would break too many Python applications.

*If* we decide to expose the command line parameter in Python, we can
add a new variable like sys.command for example. "command" name in
used in the C code of Python, and also comes from "c" of "-c".

[krivushinme]

Hello, I have find some workaround to get actual argv, but it broken:

python -c 'import ctypes; argv = ctypes.POINTER(ctypes.c_char_p)(); argc = ctypes.c_int(); ctypes.pythonapi.Py_GetArgcArgv(ctypes.byref(argc), ctypes.byref(argv)); print([argv[i] for i in xrange(0, argc.value)])'

And this will output:
['python', '-c', '-c']

May be we just need to fix this behaviour, due this is error, as far as i can see. But may broke something.

[jgehrcke]

Victor,

I support the idea of sys.command. However, it would be unpopulated most of the time (e.g. set to None by default). Now, is that something we should push forward or not? I would work on a patch, but we should have an agreement first, I guess.

Mihail,

the original argv becomes modified in the very early bootstrap phase, and the command gets lost within that process: it gets *overwritten* with "-c", which is exactly why you are observing two "-c". This happens here:

https://hg.python.org/cpython/file/default/Modules/main.c#l684

So, no, without a code change in main.c there will be no way to retain the command for later usage.

[krivushinme]

Jan-Philip, yes, I see that Main.c needs modification, but we can fix orig_argv with not just assignment but with full copy. So then we can get unmodified argv.

[zware]

Rather than add a variable to sys that will be empty 99% of the time, I think I'd rather stick a '__command__' constant in the __main__ module namespace when running with '-c' (think of '__file__'). You could then get at it elsewhere with 'from __main__ import __command__' (probably wrapped in a try/except ImportError, since it will usually not exist).

This should probably be discussed on python-ideas.

(Removing all versions but 3.5, as this is a feature request.)

[vstinner]

I marked bpo-29857 as a duplicate of this issue.

[vstinner]

See also bpo-14208 "No way to recover original argv with python -m". For the specific case of python -m, the original argument has been available as __main__.__spec__.name since Python 3.4.

[vstinner]

Many names have been proposed:

• sys.__argv__: https://bugs.python.org/issue14208#msg155002
• sys.argv_original: https://bugs.python.org/issue14208#msg155053
• sys.full_argv or sys.executable_argv: https://bugs.python.org/issue14208#msg155102
• sys.executable_argv: https://bugs.python.org/issue29857 (issue title)
• sys._executable_argv: https://bugs.python.org/issue29857#msg289938
• sys._configuration.raw_argv: https://bugs.python.org/issue14208#msg179845
• sys.raw_argv: https://bugs.python.org/issue14208#msg179852
• sys.raw_args: https://bugs.python.org/issue29857#msg289933
• sys._raw_argv: https://bugs.python.org/issue29857#msg289873
• sys.orig_arv: https://bugs.python.org/issue29857#msg289936

I chose "sys.orig_argv" attribute name with the documentation:

The list of the original command line arguments passed
to the Python executable.