Simple brute force of ideal amount of credits to add to OVH public cloud that minimises wasted credits with a monthly service

ovh-ideal-brute.py

# OVH only lets you add integer values of credits at a time,
# but credits expire 13 months after being purchased.
# So, given the monthly cost of the service and a current balance of credits
# (possibly smaller than the monthly cost) there exists an amount of added credits 
# that will yield the lowest amount of leftover credits when the the balance becomes
# lower than the monthly cost.
#
# There's probably a smarter way to do this but this is computationally cheap enough that I
# really don't care.

import math # needed for math.ceil/math.floor

# current balance (any leftover credits you currently have):
CUR_BAL = 0.00

# monthly cost:
MONTH_COST = 4.34

# range of added integer credits to score.
# no point scoring values lasting less than 3 months (because IMO I'd have to refill too often)
# nor exceeding 12 months (or any leftover credits will expire before they could be used)
CREDIT_RANGE = range(math.ceil(MONTH_COST*3 - CUR_BAL), math.ceil(MONTH_COST*13 - CUR_BAL))

# original REPL one-liner for history's sake:
# print(sorted([(x, (x + CUR_BAL) / MONTH_COST) for x in CREDIT_RANGE], key=lambda a: a[1] % 1))

# produce a list of tuples, where the first element is the number of credits to add, and the
# secondelement is leftover credits when the the balance falls below the monthly cost.

results = [(x, (x + CUR_BAL) % MONTH_COST) for x in CREDIT_RANGE]

# this list is then sorted (ascending) by the amount of leftover credits

results.sort(key=lambda a: a[1])

# finally, print the results.
# the number of months this amount will provide before running out again is also calculated.
# only the most efficient value for a given amount of months will be printed, any less efficient
# versions for the same number of months will be skipped.

seen_months = set()
for (added, leftover) in results:
    months = math.floor((added + CUR_BAL) / MONTH_COST)
   
    # only print a value for this number of months if we haven't yet printed a more efficient one.
    if months not in seen_months:
        seen_months.add(months)
        print("${:<3} credits will provide {:2} months with ${:<4.2f} left over."\
                .format(added, months, leftover))