title: difference between two regular expressions: [abc]+ and ([abc])+
body: <pre><code>In [29]: re.findall("([abc])+","abc")
  Out[29]: ['c']
  
  In [30]: re.findall("[abc]+","abc")
  Out[30]: ['abc']
  </code></pre>
  
  <p>Confused by the grouped one. How does it make difference?</p>