[Python-Dev] subprocess insufficiently platform-independent?

[Mark Hammond]

Guido quotes a colleague:

> """
> Given a straightforward command list like:
> 
>     cmd = ['svn', 'ls', 'http://rietveld.googlecode.com/svn/trunk']
> 
> You apparently cannot pass this list to any subprocess function
> (subprocess.call() or otherwise) with a set of arguments that allow it
> to "just work" on both Windows and non-Windows systems.
> 
> If you call:
> 
>     subprocess.call(cmd, shell=False)
> 
> Then it works on Linux, but fails on Windows because it does not
> perform the Windows %PATHEXT% search that allows it to find that
> "svn.exe" is the actual executable to be invoked.

I can't reproduce this as described.

>>> subprocess.call(['svn', 'ls'], shell=False)
svn: '.' is not a working copy
1

The reason this works is that Windows itself (CreateProcess) has support
both for implied '.exe' extensions and searching $PATH.  Thus, PATHEXT
handling isn't required for executables.

I *can* reproduce with another extension - eg, 'svn.py' - for this test I
had a 'foo.py' on my PATH (but not in the cwd), and .py in PATHEXT.

>>> import subprocess
>>> subprocess.call(['foo'], shell=False)
... fails
>>> subprocess.call(['foo'], shell=True)
Hello
0

So I can't see this problem for 'svn.exe' and at face value the behaviour on
Windows looks quite correct - you *do* need the shell for this functionality
on Windows (in the same way you would to execute a .bat file, for example)

> If you call:
> 
>     subprocess.call(cmd, shell=True)
> 
> Then it works on Windows (it finds the "svn.exe" executable), but it
> fails on Linux because it *only* executes the first argument in the
> list ("svn") and does not pass the remaining arguments in the list to
> the "svn" invocation.

It sounds like in this particular example at least, this behaviour on Linux
is the problem?

Mark