[Tutor] subprocess not returning

shawn wilson ag4ve.us at gmail.com
Tue Apr 22 21:49:47 CEST 2014

On Tue, Apr 22, 2014 at 3:10 PM, Alan Gauld <alan.gauld at btinternet.com> wrote:

> We have no clue what you are doing. You say "this works"
> but we can't see what 'this' is. Is the code on the
> pastebin link the working or the broken version?

Per what is expected output (which I forgot to provide - sorry about
that). Should be something like this:
  ['/testroot', '0', '0', '777'],
  ['/bin/dash', 0, 0, '755'],
  ['/lib/x86_64-linux-gnu/libc.so.6', '0', '0', '777'],
  ['/lib64/ld-linux-x86-64.so.2', '0', '0', '777'],
  ['/lib/x86_64-linux-gnu/libc-2.17.so', '0', '0', '755'],
  ['/lib/x86_64-linux-gnu/ld-2.17.so', '0', '0', '755']

Ie, find libraries a program is linked against (just try ldd against
any file because I'm not caring about optimizing at this point) and
then find the permissions of them and follow symlinks and do the same.

Though, what I'm asking specifically is why __ldd isn't returning any
values in my module.

The best I can simplify to show the part working that should also be
working in the gist code is:
import subprocess
import sys
import pprint
pp = pprint.PrettyPrinter(indent=4)

class T:
  def ldd(filename):
    libs = []
    for x in filename:
      p = subprocess.Popen(["ldd", x],

      for line in p.stdout:
        s = line.split()
        if "=>" in s:
          if len(s) == 3: # virtual library
          if len(s) == 2:

    return libs

if __name__ == "__main__":
  t = T
  fattr = [
  pp.pprint(["OUT", t.ldd(fattr)])

Past this, I can see that the ldd method is being called in my actual
code but nothing is being returned from it like it is here.

> It's also a very long listing. Can you produce a shorter
> example, perhaps with hard coded values that exhibits
> the problem?

I really did try to simplify t.py (where all of the data is included
in the script). I guess the reason for my question is because I'm not
sure what's not working or what to try next?

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