title: pack and unpack at the right format in python
body: <p>I'm looking to unpack from a buffer a string and its length.</p>
  
  <p>For example to obtain <code>(4, 'Gégé')</code> from this buffer :<br>
  <code>b'\x00\x04G\xE9g\xe9'</code></p>
  
  <p>Does someone know how to do ?</p>