hotel_stay.py

# The point of this program is to demonstrate why
# supporting negative indices can be error-prone.
# 
# The example was voluntarily made simple.
# Of course this is not the most optimized algorithm to answer 
# the question...
#
# Real life example are typically more intricate
# and may occur sporadically.
def longest_stay(hotel_rates, budget):
    """ Given the list of hotel rates for the month of august,
    return the longest affordable stay ending Sept. 1st.
    - hotel_rates: list of length 31
    - budget: maximum cost of the stay.
    """
    max_so_far = 0
    for num_days in range(31):
        if sum(hotel_rates[-num_days:]) > budget:
            # This is overbudget!
            return max_so_far
        max_so_far = num_days 
    # We can afford 
    return 31

print("result", longest_stay([10] * 31, 100))