title: change directory in os.system
body: <p>How should I use os.system to run script for several directories. 
  I tried this: </p>
  
  <pre><code>listofdirnumbers = [1, 2, 3, 4, 5]
  for i in range(len(listofdirnumbers)):
      os.system("script.py 'arg1 "mydir_%d"%i arg2 '")
  </code></pre>
  
  <p>But it gave me the error of invalid syntax.</p>
  
  <p>Another question how does it work if I want to input several arguments - is this correct? </p>
  
  <pre><code>(os.system("script.py 'arg1 arg2 arg3'"))
  </code></pre>