title: How many displayable characters in a unicode string (Japanese / Chinese)
body: <p>I'd need to know how many displayable characters are in a unicode string containing japanese / chinese characters.</p>
  
  <p>Sample code to make the question very obvious :</p>
  
  <pre><code># -*- coding: UTF-8 -*-
  str = '\xe7\x9d\xa1\xe7\x9c\xa0\xe6\x99\x82\xe9\x96\x93'
  print len(str)
  </code></pre>
  
  <p>12</p>
  
  <pre><code>print str
  </code></pre>
  
  <p>睡眠時間   &lt;&lt;&lt;
  note that four characters are displayed</p>
  
  <p>How can i know, from the string, that 4 characters are going to be displayed ?</p>