title: return the difference between maximum and minimum value of float items in a list
body: <p>I am trying to return the difference of max and min of float items in the sequence. The output shall be an int, but the algorithm given below returns a list instead. Could someone let me know what I am missing?</p>
  
  <pre><code>def flatten(*args):
      res = []
      for el in args:
          if isinstance(el,(tuple)):
              if el != ():
                  res.extend(flatten(*el))
                  continue
              else:
                  return "Empty"
          res.append(el)
      diff = [max(res)-min(res)]
      return diff
  &gt;&gt;&gt; a
  (1, 2)
  &gt;&gt;&gt; b
  (1, (7, 8))
  &gt;&gt;&gt; flatten(a,b)
  [1]
  </code></pre>