title: How to split string at regular intervals in Python 3
body: <p>I need to split a string at a regular interval and return a string with the same characters (one space and letters) with newlines at each interval so it gets to represent some kind of row/column rectangular-shaped string. I needs to return something as follows (example):</p>
  
  <pre><code>&gt;&gt;&gt; s = 'sliding puzzles'
  &gt;&gt;&gt; puzzle(s, 3, 5)
  'slidi
  ng pu
  zzles'
  </code></pre>
  
  <p>Anyone?</p>