Basic commission payment thing

commission.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
Assume a target number and an actual number
Assume a range of commission payments based upon the percentage achieved
What is the amount of commission due?
"""

from decimal import Decimal


def commission_due(ach, targ, com):
    """ calculate commission due
    args: achieved number, target number, dict w/commission bands and amounts
    """
    if ach <= 0:
        return 0
    # work out the percentage achieved
    perc = int(round((float(ach) / float(targ)) * 100, 0))
    for k in sorted(com.iterkeys(), reverse = True):
        if perc < k:
            # we haven't reached a matching band yet
            continue
        # found a band >= perc, or the highest key value
        else:
            return ach * com[k]
    # return the lowest band
    return ach * com[min(com.iterkeys())]


commissions = {
        110: Decimal(12),
        100: Decimal(10),
        75: Decimal(7.50),
        50: Decimal(5),
        20: Decimal(2)}

target = 456
achieved = 3

print commission_due(achieved, target, commissions)
# 68%, '50%' band, commission: 1560