calling subprocess

[jkuplinsky at gmail.com]

On Sunday, February 22, 2015 at 5:22:24 PM UTC-5, Chris Angelico wrote:
> On Mon, Feb 23, 2015 at 9:06 AM,  <jkuplinsky at gmail.com> wrote:
> > I thought this would be easy:
> >
> >
> > for subprocess import call
> > call (['cd', r'C:\apps'], shell = True)
> >
> >
> > It doesn't work -- tried with/without prefix r, escaped backslashes, triple quotes, str(), .. nothing seems to work (it doesn't complain, but it doesn't change directories either) -- what am I doing wrong?
> 
> It does work. But what it does is spawn a shell, change the working
> directory _of that shell_, and then terminate it. The working
> directory change won't apply to your process.
> 
> It sounds to me like you're adopting a "shotgun debugging" [1]
> approach. If you don't know what your changes are going to do, why are
> you making them? I recommend, instead, a policy of examination and
> introspection - what I tend to refer to as IIDPIO debugging: If In
> Doubt, Print It Out. The first argument to subprocess.call() is a list
> of parameters; you can assign that to a name and print it out before
> you do the call:
> 
> from subprocess import call
> args = ['cd', r'C:\apps']
> print(args)
> call(args, shell=True)
> 
> Now do all your permutations of args, and see what effect they have.
> If the printed-out form is identical, there's no way it can affect the
> subprocess execution.
> 
> Side point: *Copy and paste* your code rather than retyping it. The
> keyword here is "from", not "for", and if we can't depend on the code
> you're showing us, how can we recognize whether or not a bug exists in
> your real code?
> 
> ChrisA
> 
> [1] http://www.catb.org/jargon/html/S/shotgun-debugging.html

OK (1) sorry about for/from
(2) print() sounds nice, but fact is , no matter what I try, i always get C:\\apps instead of c:\apps. So in this sense print() doesn't help much. Obviously i'm doing something wrong -- which is what you perhaps call shotgun debugging; but that's why i'm asking.