title: python empty argument
body: <p>how do I print help info if no arguments are passed to python script?</p>
  
  <pre><code>#!/usr/bin/env python
  
  import sys
  
  for arg in sys.argv:
      if arg == "do":
          do this
      if arg == ""
          print "usage is bla bla bla"
  </code></pre>
  
  <p>what I'm missing is <code>if arg == ""</code> line that I don't know how to express :( </p>