heapify returns NoneType
<p>I have</p>

<pre><code>l = heapify([5,4,9,1])
</code></pre>

<p>and if I do a </p>

<pre><code>type(l)
</code></pre>

<p>It says it's NoneType instead of list type,  anyone know what I'm doing wrong??</p>
