Retrieving the full command line

Tim Golden mail at timgolden.me.uk
Thu Jan 24 16:51:33 CET 2013


On 24/01/2013 15:28, Oscar Benjamin wrote:
> On 24 January 2013 13:45, Tim Golden <mail at 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

TJG




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