title: python time(milli seconds) calculation
body: <p>How to calculate milliseconds,from the code below.</p>
  
  <pre><code>a = datetime.datetime.now()
  b = datetime.datetime.now()
  c = b - a
  
  &gt;&gt;&gt; c
  
  &gt;&gt;&gt; c.days
  0
  &gt;&gt;&gt; c.seconds
  4
  &gt;&gt;&gt; c.microseconds
  </code></pre>