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