title: Python: frame parameter of signal handler
body: <p>I was looking through the Python documentation for signal and in the example code:</p>
  
  <pre><code>def handler(signum, frame):
      print 'Signal handler called with signal', signum
      raise IOError("Couldn't open device!")
  </code></pre>
  
  <p>The 'frame' parameter is not used in the actual function. I noticed this in a lot of code on stackoverflow/online regarding signal handlers. What is the 'frame' parameter? Why is it kept in the function header?</p>
  
  <p>Thank you</p>