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Date: Thu, 24 Jan 2013 16:53:58 +0000
Subject: Re: Retrieving the full command line
From: Oscar Benjamin <oscar.j.benjamin@gmail.com>
To: Tim Golden <mail@timgolden.me.uk>
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On 24 January 2013 16:08, Oscar Benjamin <oscar.j.benjamin@gmail.com> wrote:
> On 24 January 2013 15:51, Tim Golden <mail@timgolden.me.uk> wrote:
>> On 24/01/2013 15:28, Oscar Benjamin wrote:
>>> On 24 January 2013 13:45, Tim Golden <mail@timgolden.me.uk> wrote:
>>>> On 24/01/2013 11:30, Oscar Benjamin wrote:
>>>>> I don't really understand what your spec is. Why do you need to
>>>>> inspect this information from sys.argv? Can you not just always use
>>>>> 'python -m pkg' as your entry point?
>>>>
>>> [SNIP]
>>>>
>>>> For completeness, I'm talking about the cherrypy Autoreloader which
>>>> attempts to restart (via execv) whatever process was responsible for
>>>> loading it in the first place, via an identical or equivalent command
>>>> line. The current (cherrypy) code simply joins sys.executable and
>>>> sys.argv but this fails in the face of python -m as we have seen.
>>>>
>>>> The cherrypy package has no especial knowledge of the structure of the
>>>> application which imported it and so must piece together the command
>>>> line somehow. Clearly, I can take various approaches of the sort
>>>> which you've outlined, or subclass the reloader, or fetch the original
>>>> command line from the OS, etc. It's not that this is a showstopper,
>>>> merely slightly surprising. (To me).
>>>
>>> Ok I understand. Then I guess you want:
>>>
>>> import __main__
>>> pkg = __main__.__package__
>>
>> Brilliant. Never thought of importing __main__. Thanks.
>>
>> For the benefit of anyone still watching, the code (which has to be
>> compatible back to 2.3) looks something like this:
>>
>> <code>
>> import __main__
>>
>> # [.. .snip ...]
>>
>> try:
>>     is_package = bool(__main__.__package__)
>> except NameError:
>>     is_package = False
>> if is_package:
>>     args = [sys.executable, '-m', __main__.__package__] + sys.argv[1:]
>> else:
>>     args = [sys.executable] + sys.argv
>>
>> os.chdir(_startup_cwd) # avoids relative/absolute issues
>> os.execv(args[0], args)
>>
>> </code>
>>
>> I don't pretend it's foolproot, but it certainly works for my particular
>> case. Nor have I considered it against all the cases identified in PEP
>> 432: http://www.python.org/dev/peps/pep-0432/#configuring-sys-argv
>
> Does it work if you use the -m option to run a module rather than a script?

Sorry that was written incorrectly. I meant to say: does it work when
a module is directly on sys.path rather than as a submodule of a
package? In this case __package__ is set to the empty string if run
with -m or None if run with a direct path. So the check needs to be
"__package__ is not None" rather than "bool(__package__)".


Oscar