title: Why this shows "string index out of range sometimes"?
body: <p>I run this code in a loop with different length of father[0] value each time. All works well but sometimes it pops the error "String index out of range"</p>
  
  <pre class="lang-py prettyprint-override"><code>for a in range(len(father[0])):
  
          column = [item[a] for item in father]
  </code></pre>