new_contents: # http://rightfootin.blogspot.com/2006/09/more-on-python-flatten.html
  def flatten(l, ltypes=(list, tuple)):
      if l is None:
          return []
      if not isinstance(l, ltypes):
          return [l]
  
      ltype = type(l)
      l = list(l)
      i = 0
      while i < len(l):
          while isinstance(l[i], ltypes):
              if not l[i]:
                  l.pop(i)
                  i -= 1
                  break
              else:
                  l[i:i + 1] = l[i]
          i += 1
      return ltype(l)
  
subject: Add missing flatten function