title: Python os.path.walk() method
body: <p>I'm currently using the <code>walk</code> method in a uni assignment. It's all working fine, but I was hoping that someone could explain something to me. </p>
  
  <p>in the example below, what is the <code>a</code> parameter used for on the <code>myvisit</code> method? </p>
  
  <pre><code>&gt;&gt;&gt; from os.path import walk
  &gt;&gt;&gt; def myvisit(a, dir, files):
  ...   print dir,": %d files"%len(files)
  
  &gt;&gt;&gt; walk('/etc', myvisit, None)
  /etc : 193 files
  /etc/default : 12 files
  /etc/cron.d : 6 files
  /etc/rc.d : 6 files
  /etc/rc.d/rc0.d : 18 files
  /etc/rc.d/rc1.d : 27 files
  /etc/rc.d/rc2.d : 42 files
  /etc/rc.d/rc3.d : 17 files
  /etc/rc.d/rcS.d : 13 files
  </code></pre>