Python loop practice
<p>I'm practicing loops. I've been trying to figure out how to get each character printed 4 times and place aside the others, eg: aaaaccccddddcccc. Right now the returned res is only showing me the last character printed 4 times (cccc). I tried nested  for loops but that wasn't working for me either. How do I concatenate the returns? (or is there another way) </p>

<pre><code>def quad_char(letter):
  res = ''
  for i in letter:
    res = i * 4
  return res

print(quad_char('acdc'))
</code></pre>