title: Pandas filter rows based on multiple conditions
body: <p>I have some values in the <code>risk</code> column that are neither, <code>Small</code>, <code>Medium</code> or <code>High</code>. I want to delete the rows with the value not being <code>Small</code>, <code>Medium</code> and <code>High</code>. I tried the following:</p>
  <pre><code>df = df[(df.risk == &quot;Small&quot;) | (df.risk == &quot;Medium&quot;) | (df.risk == &quot;High&quot;)]
  </code></pre>
  <p>But this returns an empty DataFrame. How can I filter them correctly?</p>