Expand pandas DataFrame column into multiple rows : <p>If I have a <code>DataFrame</code> such that:</p>

<pre><code>pd.DataFrame( {"name" : "John", 
               "days" : [[1, 3, 5, 7]]
              })
</code></pre>

<p>gives this structure:</p>

<pre><code>           days  name
0  [1, 3, 5, 7]  John
</code></pre>

<p>How do expand it to the following?</p>

<pre><code>   days  name
0     1  John
1     3  John
2     5  John
3     7  John
</code></pre>
