How to add index into a dict
<p>For example, given:</p>

<pre><code>['A', 'B', 'A', 'B']    
</code></pre>

<p>I want to have:</p>

<pre><code>{'A': [0, 2], 'B': [1, 3]}
</code></pre>

<p>I tried a loop that goes like; add the index of where the character is found, then replace it with <code>''</code> so the next time the loop goes through, it passes on to the next character. </p>

<p>However, that loops doesn't work for other reasons, and I'm stuck with no idea how to proceed.</p>