title: Powerset recursive, list comprehension python3
body: <p>I'm new to Python3 and are trying to do a recursive powerset function. It should use list comprehension. </p>
  
  <p>I wrote:</p>
  
  <pre><code>def powerset(seq):
      if not seq:
         return [[]]
      return powerset(seq[1:]) + [[seq[0]] + n for n in powerset(seq[1:])]
  </code></pre>
  
  <p>This function works but I got feedback and was told it was unnecessary to call the function two times. It did to much computing. It should easily be able to compute up to 20 powersets. So how should I do? I can't get it to work without calling the function twice. Thanks.</p>