What gets returned is the return value of executing this command. What you see in while executing it directly is the output of the command in stdout. That 0 is returned means, there was no error in execution.
Use popen etc for capturing the output .
Some thing along this line:
import subprocess as sub
p = sub.Popen(['your command', 'arg1', 'arg2',...],stdout=sub.PIPE,stderr=sub.PIPE)
output, errors = p.communicate() print output
p = os.popen('command',"r")
line = p.readline()
if not line: