[Python-Dev] subprocess.Popen and win32

[Victor Stinner]

On Python 3, you can use Unicode on all platforms. On UNIX, there is no
need to encode explicitly.

Victor
Le 20 avr. 2014 04:17, "David Aguilar" <davvid at gmail.com> a écrit :

> Hi,
>
> I just joined python-dev because I found the need to add some code to
> paper over python3's subprocess API, and I'm wondering whether I'm
> missing something.
>
> On python2 and python3, the (only?) way to get utf-8 arguments to
> subprocess was to ensure that all unicode strings are encoded into
> bytes before subprocess sees them. This has worked for a long time
> (currently compatible across python2 and 3).
>
> On python3, this still works for normal platforms, but on windows we
> can't pass a list of byte strings. We have to pass a list of unicode
> strings.
>
> This means that the application code ends up needing to do this:
>
> https://github.com/git-cola/git-cola/commit/1109aeb4354c49931d9b0435d2b7cfdc2d5d6966
>
> basically,
>
> def start_command(cmd):
>     if sys.platform == 'win32':
>         # Python on windows always goes through list2cmdline() internally
> inside
>         # of subprocess.py so we must provide unicode strings here
> otherwise
>         # Python3 breaks when bytes are provided.
>         cmd = [decode(c) for c in cmd]
>     else:
>         cmd = [encode(c) for c in cmd]
>      return subprocess.Popen(cmd)
>
> That seems broken to me, so I wonder if this is a bug in the way
> python3 is handling Popen with list-of-bytestring on win32?
>
> I'm not a windows user, but I was able to install python3 under wine
> and the same traceback happens without the paper bag fix. This is what
> the traceback looks like; it dies in list2cmdline (which I am not
> calling directly, Popen does it under the covers):
>
>     File "E:\Program Files
> (E)\git-cola\share\git-cola\lib\cola\core.py", line 109, in
> start_command
>     universal_newlines=universal_newlines)
>     File "C:\Python32\lib\subprocess.py", line 744, in __init__
>     restore_signals, start_new_session)
>     File "C:\Python32\lib\subprocess.py", line 936, in _execute_child
>     args = list2cmdline(args)
>     File "C:\Python32\lib\subprocess.py", line 564, in list2cmdline
>     needquote = (" " in arg) or ("\t" in arg) or not arg
>     TypeError: Type str doesn't support the buffer API
>
> This is an issue for folks that use python to write cross-platform
> code. The unix code paths expect list-of-bytes, but win32 only expects
> list-of-unicode, which pushes the burden onto the application
> programmer.
>
> It's my opinion that the win32 code path on python3 is the odd man
> out. If it allowed list-of-bytes like python2/win32 and python2+3/unix
> then this wouldn't be an issue.
>
> Is this an actual problem, or is it something that should be handled
> by application-level code as I've done?
>
> Thanks,
> --
> David
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