title: Why is this lookbehind failing and what does this exception mean?
body: <p>I'm trying get all ID numbers preceded by some specific text, but it returns nothing followed by an exception (<code>"Exception AttributeError: "'NoneType' object has no attribute 'path'" in &lt;function _remove at 0x01F68530&gt; ignored"</code>)</p>
  
  <pre><code>f = open('log.txt')
  s = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
  a = re.compile('(?&lt;=Activating user record[\s\S]{98})[\w]{15}')
  ids = re.findall(a, s)
  print ids
  </code></pre>
  
  <p>The pattern works when I test it. If I remove the lookbehind assertion or use another pattern, it's finding matches e.g. re.compile('[\w]{15}'). What am I missing?</p>
  
  <p>I'm trying to snag the 15 character ID from something like this: <a href="https://regex101.com/r/1JKo6O/2" rel="nofollow noreferrer">https://regex101.com/r/1JKo6O/2</a></p>