title: TypeError: 'str' object does not support item assignment (Python)
body: <p>So this is what I'm trying to do:</p>
  <p>input: ABCDEFG</p>
  <p>Desired output:</p>
  <pre><code>***DEFG
  A***EFG
  AB***FG
  ABC***G
  ABCD***
  </code></pre>
  <p>and this is the code I wrote:</p>
  <pre><code>def loop(input):
      output = input
      for index in range(0, len(input)-3):              #column length
          output[index:index +2] = '***'
          output[:index] = input[:index]
          output[index+4:] = input[index+4:]
          print output + '\n'
  </code></pre>
  <p>But I get the error: <code>TypeError: 'str' object does not support item assignment</code></p>