docs: def createProduct(self, powerups):
          """
          Create a new L{Product} instance which confers the given
          powerups.
  
          @type powerups: C{list} of powerup item types
  
          @rtype: L{Product}
          @return: The new product instance.
          """
          types = [qual(powerup).decode('ascii')
                         for powerup in powerups]
          for p in self.store.parent.query(Product):
              for t in types:
                  if t in p.types:
                      raise ValueError("%s is already included in a Product" % (t,))
          return Product(store=self.store.parent,
                         types=types)