[Python-Dev] Re: subprocess - updated popen5 module

Jason Lunz lunz at falooley.org
Sun Oct 10 15:17:41 CEST 2004

pf_moore at yahoo.co.uk said:
> Hence on Windows, a command line is the fundamental unit, whereas on
> Unix an argument list is fundamental.

Yes, you're right. I read up on CreateProcess(), GetCommandLine(), and
CommandLineToArgvW() after posting. Interestingly, MS's sample code for
CommandLineToArgvW is buggy because of confusion between the two


Also, it can fail.

> The biggest problem on Windows is that not all executables use the
> Microsoft C runtime. Some use other C runtimes, others parse the
> command line directly and don't use argv at all.

So why does subprocess use cmdline2list() in the parent on unix to
emulate the way a child subprocess might parse the string on windows?
(But only if it's written in C, uses the MSC runtime, and uses the
argv/argc handed to main() rather than calling GetCommandLine() itself).
Why not emulate CommandLineToArgvW()? or something else entirely? I
think it would be cleaner not to emulate anything at all.

> The unix execv is just *different*. Both the Windows and the Unix
> interfaces have capabilities the other doesn't offer.

Well, the windows interface is a subset of the unix one. The length of
argv on windows is limited to 1.

> I think Peter's approach of supporting both forms - a single string as
> a command line, and list of strings as an argv list, and converting
> both to the more natural OS-native form as needed, is sensible (I
> would, I argued for it when he was developing it!)

I can see that it's trying to be symmetric and orthogonal, but I don't
think that the result is worth it in this case. In what scenario is the
use of cmdline2list() really useful?


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