title: Check if list contains element different from something
body: <p>Is there an efficient way of checking if a list contains an element which is not a certain element like the other ones?</p>
  <p>I have many lists looking like that:</p>
  <pre><code>a = [&quot;_&quot;, &quot;_&quot;, &quot;_&quot;, &quot;_&quot;]
  b = [&quot;_&quot;, &quot;b&quot;, &quot;_&quot;, &quot;_&quot;]
  c = [&quot;a&quot;, &quot;_&quot;, &quot;x&quot;, &quot;_&quot;]
  </code></pre>
  <p>They are mostly underscores but sometimes there is an element not being an underscore. I only want to process those with &quot;content&quot;. At the moment, I do that with for-loops checking if there is a non-underscore element.
  Is there a more efficient way?</p>