code: def count_items(self, unique=True):
          
          if unique:
              return len(self.items)
          return sum([item.quantity for item in self.items.values()])
docs: Count items in the cart.
  
          Parameters
          ----------
          unique : bool-convertible, optional
  
          Returns
          -------
          int
              If `unique` is truthy, then the result is the number of
              items in the cart. Otherwise, it's the sum of all item
              quantities.