#!/usr/bin/env python3
units = [0.5, 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000]

def calculate(price, paid):
    print("pris: {} betalt: {}".format(price, paid))
    byttepenge = paid - price
    afrundet = round(byttepenge * 2, 0)/2
    if byttepenge != afrundet:
        print("afrundet fra {} til {}".format(byttepenge, afrundet))
    print("byttepenge: {}".format(afrundet))
    returned = returnUnits(afrundet, [])
    print("mønter/sedler retur: {}\n".format(returned))

def returnUnits(amount, returned = []):
    for unit in units[::-1]:
        if amount in units:
            returned.append(amount)
            return returned
        left = unit - amount
        if left <= 0:
            returned.append(unit)
            return returnUnits(abs(left), returned)

calculate(0.15, 10.0)
calculate(39, 80)