title: Regular expression for repeating sequence
body: <p>I'd like to match three-character sequences of letters (only letters 'a', 'b', 'c' are allowed) separated by comma (last group is not ended with comma).</p>
  
  <p>Examples:</p>
  
  <pre><code>abc,bca,cbb
  ccc,abc,aab,baa
  bcb
  </code></pre>
  
  <p>I have written following regular expression:</p>
  
  <pre><code>re.match('([abc][abc][abc],)+', "abc,defx,df")
  </code></pre>
  
  <p>However it doesn't work correctly, because for above example:</p>
  
  <pre><code>&gt;&gt;&gt; print bool(re.match('([abc][abc][abc],)+', "abc,defx,df")) # defx in second group
  True
  &gt;&gt;&gt; print bool(re.match('([abc][abc][abc],)+', "axc,defx,df")) # 'x' in first group
  False
  </code></pre>
  
  <p>It seems only to check first group of three letters but it ignores the rest. How to write this regular expression correctly?</p>