title: Pandas: how to drop rows if contains more that 2 entries?
body: <p>I have a dataframe like the following</p>
  
  <pre><code>df
          entry
  0       (5, 4)
  1       (4, 2, 1)
  2       (0, 1)
  3       (2, 7)
  4       (9, 4, 3)
  </code></pre>
  
  <p>I would like to keep only the <code>entry</code> that contains two values</p>
  
  <pre><code>df
       entry
  0    (5, 4)
  1    (0, 1)
  2    (1, 7)
  </code></pre>