title: What does sentence[:] mean here?
body: <p>I'm study Learnpythonthehardway, in ex40, I met this slice of code.</p>
  
  <pre><code>for sentence in snippet, phrase:
      result = sentence[:]
  </code></pre>
  
  <p>I'm not quite understanding sentence[:] here, especially the [:]</p>
  
  <p>I've tried to figure it out by underlying test code:</p>
  
  <pre><code>sentence = 'sss errf : fe : eee'
  f = 33
  result = sentence[:f]
  print result
  </code></pre>
  
  <p>but nothing happens, result is the same as the sentence</p>
  
  <p>So, smart geeks, what does sentence[:] mean here?</p>