title: regex matching complete expression containing multiple, similar terms
body: <p>I have a string. For example:</p>
  
  <pre><code>s = "caption = #1081#1082#1083#1084', '#1087#1088 efiuefiu #23   3456"
  </code></pre>
  
  <p>I need to find all expressions consists of # and 4 digits, but I need to find expression <code>#1081#1082#1083#1084</code>, not <code>#1081</code>, <code>#1082</code>, <code>#1083</code> and <code>#1084</code> separately like this.</p>
  
  <p>This doesn't work; it matches the individual expressions:</p>
  
  <pre><code>result = re.findall(r'#\d{4}', s)
  </code></pre>