title: Only if I'm not using __iadd__, I get TypeError: can only concatenate list (not "str") to list
body: <p>Why does this work ...</p>
  <pre class="lang-py prettyprint-override"><code>&gt;&gt;&gt; a = [0, 1, 2]
  &gt;&gt;&gt; a += &quot;x&quot; * 3
  &gt;&gt;&gt; a
  [0, 1, 2, 'x', 'x', 'x']
  </code></pre>
  <p>... but this doesn't?</p>
  <pre class="lang-py prettyprint-override"><code>&gt;&gt;&gt; [0, 1, 2] + &quot;x&quot; * 3
  Traceback (most recent call last):
    File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
  TypeError: can only concatenate list (not &quot;str&quot;) to list
  </code></pre>