title: Convert a dataframe to list of tuples
body: <p>I have a python pandas dataframe df like this:</p>
  
  <pre><code>a  b
  1  3
  3  6
  5  7
  6  4
  7  8
  </code></pre>
  
  <p>I want to transfer it to a list:</p>
  
  <pre><code>[(1,3),(3,6),(5,7),(6,4),(7,8)]
  </code></pre>
  
  <p>Thanks.</p>