title: Python function parameter ([x[,y[,z]]]) meaning
body: <p>I have come across this kind of method signature in python docs. What does it mean? eg. </p>
  
  <pre><code>smtplib.SMTP([host[, port[, local_hostname[, timeout]]]]
  </code></pre>
  
  <p>In general syntax such as <code>function([x[,y[,z]]])</code>?</p>