title: utf-8 plus question marks
body: <p>I have a site that displays user input by decoding it to unicode using utf-8. However, user input can include binary data, which is obviously not always able to be 'decoded' by utf-8.</p>
  
  <p>I'm using Python, and I get an error saying:</p>
  
  <blockquote>
    <p>'utf8' codec can't decode byte 0xbf in position 0: unexpected code byte. You passed in '\xbf\xcd...</p>
  </blockquote>
  
  <p>Is there a standard efficient way to convert those undecodable characters into question marks?</p>
  
  <p>It would be most helpful if the answer uses Python.</p>