title: decode(unicode_escape) in python 3 a string
body: <p>I've checked <a href="https://stackoverflow.com/questions/14820429/how-do-i-decodestring-escape-in-python3">this solution</a> but it doesn't work in python3.</p>
  
  <p>I've an escaped string of this kind: <code>str = "Hello\\nWorld"</code> and I want to obtain the same string unescaped: <code>str_out = Hello\nWorld</code></p>
  
  <p>I tried with this without succes: <code>AttributeError: 'str' object has no attribute 'decode'</code></p>
  
  <p>Here my sample code: </p>
  
  <pre><code>str = "Hello\\nWorld"
  str.decode('unicode_escape')
  </code></pre>