title: what does print(s%%s) mean here?
body: <pre><code>s='s=%r;print(s%%s)';print(s%s)
  </code></pre>
  
  <p>I understand % is to replace something in a string by s (but actually who to replace?)
  Maybe more intriguing is, why the <code>print(s%%s)</code> become <code>print(s%s)</code> automatically after <code>%s</code> is replaced by <code>s</code> itself?</p>