old_contents: BOOK_PRICE = 8
  
  
  def _group_price(size):
      discounts = [0, .05, .1, .2, .25]
      if not (0 < size <= 5):
          raise ValueError('size must be in 1..' + len(discounts))
      return 8 * size * (1 - discounts[size - 1])
  
  
  def calculate_total(books, price_so_far=0.):
      if not books:
          return price_so_far
  
      groups = list(set(books))
      min_price = float('inf')
  
      for i in range(len(groups)):
  
          remaining_books = books[:]
  
          for v in groups[:i + 1]:
              remaining_books.remove(v)
  
          price = calculate_total(remaining_books,
                                  price_so_far + _group_price(i + 1))
          min_price = min(min_price, price)
  
      return min_price
  
new_contents: BOOK_PRICE = 8
  
  
  def _group_price(size):
      discounts = [0, .05, .1, .2, .25]
      if not (0 < size <= 5):
          raise ValueError('size must be in 1..' + len(discounts))
      return BOOK_PRICE * size * (1 - discounts[size - 1])
  
  
  def calculate_total(books, price_so_far=0.):
      if not books:
          return price_so_far
  
      groups = list(set(books))
      min_price = float('inf')
  
      for i in range(len(groups)):
  
          remaining_books = books[:]
  
          for v in groups[:i + 1]:
              remaining_books.remove(v)
  
          price = calculate_total(remaining_books,
                                  price_so_far + _group_price(i + 1))
          min_price = min(min_price, price)
  
      return min_price
  
subject: use book price const in calculation