change_o_matic.py

def change_o_matic(price, amount_paid):
	amount_due = amount_paid - price
	if amount_due < 0:
		raise ValueError("amount paid ({0}) must not be less than price ({1}) ".format(amount_paid, price))

	change = {1000: 0, 500: 0, 200: 0, 100: 0, 
	          50: 0, 20: 0, 10: 0, 5: 0, 2: 0, 1: 0 }
	denominations = sorted(change.keys(), reverse=True)
	for den in denominations:
		while amount_due >= den:
			change[den] += 1
			amount_due -= den
	return change