title: Variable within xpath is not working correctly
body: <p>This works:</p>
  <pre><code>i = 1
  num = '3.1.' + str(i)
  if (num == '3.1.1'):
      print(&quot;correct&quot;)
  </code></pre>
  <p>And this works:</p>
  <pre><code>num = '3.1.1'
  for content in tree.findall(&quot;.//Section/Section/Section[@SectionNumber='{}']&quot;.format(num)):
      print(&quot;correct&quot;)
  </code></pre>
  <p>But this doesn't work:
  (No error, just didn't print correct)</p>
  <pre><code>i = 1
  num = '3.1.' + str(i)
  for content in tree.findall(&quot;.//Section/Section/Section[@SectionNumber='{}']&quot;.format(num)):
      print(&quot;correct&quot;)
  </code></pre>
  <hr />
  <p>What is wrong when I combining the string? Thank you.</p>