Best way to rewrite Popen

[Zachary Ware]

On May 19, 2015 12:48 PM, "Chris Angelico" <rosuav at gmail.com> wrote:
>
> On Wed, May 20, 2015 at 3:01 AM, Cecil Westerhof <Cecil at decebal.nl> wrote:
> > At the moment I am playing with things like:
> >     p = subprocess.Popen('ls -l', shell = True, stdout =
subprocess.PIPE)
> >
> > I think that most of the times this are the values I want. So it would
> > be nice to overrule the defaults. What is the best way to do this? So
> > creating a function that is exactly the same except for the defaults
> > for shell and stdout (and maybe stderr).
>
> Well... I would have to start by saying that you probably _don't_ want
> to use shell=True by default. Putting it explicitly on the cases where
> you need it helps you remember its danger. You also don't need it for
> simple cases like that one; improve your reliability by providing a
> list instead of a string, and then you can leave shell=False:
>
> p = subprocess.Popen(['ls','-l'], stdout=subprocess.PIPE)
>
> Running everything via the shell is unnecessary, and a dangerous
> default. (Maybe it's not a problem when you use a string literal as
> the command, but if you make that the default, you'll end up exposing
> yourself in some situation where it isn't hard-coded.) With that
> change, there's really only one parameter that you're defaulting, so
> there's not as much point making the change, but the technique still
> works, and maybe you'll add more to the setup:
>
> @functools.wraps(subprocess.Popen)
> def Popen(*a, **kw):
>     if 'stdout' not in kw: kw['stdout'] = subprocess.PIPE
>     return subprocess.Popen(*a, **kw)
>
> That's a simple way to patch in some function defaults. But
> personally, I'd probably end up doing something like this:
>
> def capture_stdout(*a, **kw):
>     if 'stdout' not in kw: kw['stdout'] = subprocess.PIPE

Just a quick note that this line can be simplified nicely to:

kw.setdefault('stdout', subprocess.PIPE)

Regards,
--
Zach
(on a phone)
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