[issue23427] Python should expose command when invoked with -c
New submission from Jan-Philip Gehrcke: 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! ---------- assignee: docs@python components: Documentation, Interpreter Core files: sys_argv_cmd.patch keywords: patch messages: 235633 nosy: docs@python, georg.brandl, haypo, jgehrcke, pitrou priority: normal severity: normal status: open title: Python should expose command when invoked with -c type: enhancement versions: Python 3.5, Python 3.6 Added file: http://bugs.python.org/file38065/sys_argv_cmd.patch _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
STINNER Victor added the comment: 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". ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
Михаил Кривушин added the comment: 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. ---------- nosy: +Михаил.Кривушин _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
Jan-Philip Gehrcke added the comment: 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. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
Mihail Krivushin added the comment: 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. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
Changes by Mihail Krivushin <krivushinme@gmail.com>: ---------- versions: +Python 2.7, Python 3.2, Python 3.3, Python 3.4 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
Zachary Ware added the comment: 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.) ---------- assignee: docs@python -> components: -Documentation nosy: +zach.ware versions: -Python 2.7, Python 3.2, Python 3.3, Python 3.4, Python 3.6 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
Changes by R. David Murray <rdmurray@bitdance.com>: ---------- nosy: +r.david.murray _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: I marked bpo-29857 as a duplicate of this issue. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
Change by STINNER Victor <vstinner@python.org>: ---------- pull_requests: +19940 stage: -> patch review pull_request: https://github.com/python/cpython/pull/20729 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
Change by Jakub Wilk <jwilk@jwilk.net>: ---------- nosy: +jwilk _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: 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. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: 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. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: I marked bpo-15577 "Real argc and argv in embedded interpreter" as duplicate of this issue: my PR 20729 allows embedders to set PyConfig.orig_argv which becomes sys.orig_argv. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: Example of sys.orig_argv usage to re-execute the Python process with different options: --- import sys import os if not sys.flags.utf8_mode: # Force UTF-8 mode argv = sys.orig_argv.copy() argv[1:1] = ["-X", "utf8"] print(f"Re-execute to force UTF-8 mode! argv={argv}") os.execv(argv[0], argv) print(f"Everybody loves UTF-8! utf8_mode={sys.flags.utf8_mode}") --- Example coming from discussions on the PEP 597 :-) Output: --- $ ./python force_utf8_mode.py Re-execute to force UTF-8 mode! argv=['./python', '-X', 'utf8', 'force_utf8_mode.py'] Everybody loves UTF-8! utf8_mode=1 --- ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: My implementation (PR 20729) is based on bpo-40910 change which added a private PyConfig._orig_argv member to fix Py_GetArgcArgv(). ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
Change by STINNER Victor <vstinner@python.org>: ---------- title: Python should expose command when invoked with -c -> Add sys.orig_argv: original command line arguments passed to the Python executable _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
Change by STINNER Victor <vstinner@python.org>: ---------- versions: +Python 3.10 -Python 3.5 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: The setproctitle project uses Py_GetArgcArgv() and would benefit of PyConfig.orig_argv, see: * https://bugs.python.org/issue15577#msg370965 * https://github.com/dvarrazzo/py-setproctitle/issues/8 ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: New changeset dd8a93e23b5c4f9290e1cea6183d97eb9b5e61c0 by Victor Stinner in branch 'master': bpo-23427: Add sys.orig_argv attribute (GH-20729) https://github.com/python/cpython/commit/dd8a93e23b5c4f9290e1cea6183d97eb9b5... ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
STINNER Victor <vstinner@python.org> added the comment: I added sys.orig_argv to the master branch (future Python 3.10). ---------- resolution: -> fixed stage: patch review -> resolved status: open -> closed _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue23427> _______________________________________
participants (7)
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Jakub Wilk -
Jan-Philip Gehrcke
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Mihail Krivushin
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R. David Murray
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STINNER Victor
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Zachary Ware
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Михаил Кривушин