title: What does %s mean in a Python format string?
body: <p>What does <code>%s</code> mean in Python? And what does the following bit of code do?</p>
  <p>For instance...</p>
  <pre><code> if len(sys.argv) &lt; 2:
       sys.exit('Usage: %s database-name' % sys.argv[0])
  
   if not os.path.exists(sys.argv[1]):
       sys.exit('ERROR: Database %s was not found!' % sys.argv[1])
  </code></pre>