title: Regex substring one mismatch in any location of string
body: <p>Can someone explain why the code below returns an empty list:</p>
  
  <pre><code>&gt;&gt;&gt; import re
  &gt;&gt;&gt; m = re.findall("(SS){e&lt;=1}", "PSSZ")
  &gt;&gt;&gt; m
  []
  </code></pre>
  
  <p>I am trying to find the total number of occurrences of <code>SS</code> (and incorporating the possibility of <strong>up to one mismatch</strong>) within <code>PSSZ</code>.  </p>
  
  <p>I saw a similar example of code here: <a href="https://stackoverflow.com/questions/2420412/search-for-string-allowing-for-one-mismatch-in-any-location-of-the-string">Search for string allowing for one mismatch in any location of the string</a> </p>