title: Python: What's the difference between set.difference and set.difference_update?
body: <p><strong>s.difference(t)</strong> returns a new set with no elements in <strong>t</strong>.</p>
  
  <p><strong>s.difference_update(t)</strong> returns an updated set with no elements in <strong>t</strong>.</p>
  
  <p>What's the difference between these two set methods?
  Because the difference_update updates set s, what precautions should be taken to avoid receiving a result of None from this method? </p>
  
  <p>In terms of speed, shouldn't set.difference_update be faster since you're only removing elements from set s instead of creating a new set like in set.difference()?</p>