[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

STINNER Victor  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().

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[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

STINNER Victor  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
---

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[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

STINNER Victor  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.

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[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

STINNER Victor  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.

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[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

STINNER Victor  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.

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[issue23427] Python should expose command when invoked with -c

[Jakub Wilk]

Change by Jakub Wilk :


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nosy: +jwilk

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[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

Change by STINNER Victor :


--
pull_requests: +19940
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/20729

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[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

STINNER Victor  added the comment:

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

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[issue23427] Python should expose command when invoked with -c

[R. David Murray]

Changes by R. David Murray :


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nosy: +r.david.murray

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[issue23427] Python should expose command when invoked with -c

[Zachary Ware]

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

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[issue23427] Python should expose command when invoked with -c

[Mihail Krivushin]

Changes by Mihail Krivushin :


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versions: +Python 2.7, Python 3.2, Python 3.3, Python 3.4

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[issue23427] Python should expose command when invoked with -c

[Mihail Krivushin]

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.

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[issue23427] Python should expose command when invoked with -c

[Jan-Philip Gehrcke]

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.

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[issue23427] Python should expose command when invoked with -c

[Михаил Кривушин]

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.

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nosy: +Михаил.Кривушин

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[issue23427] Python should expose command when invoked with -c

[STINNER Victor]

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".

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[issue23427] Python should expose command when invoked with -c

[Jan-Philip Gehrcke]

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

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