calc.py

import csv
from calendar import monthrange

def get_n_days(year, month):
    return monthrange(year, month)[1]

def due_month(year, month):
    due_month = ((month + 6) % 12)
    if due_month == 0: due_month = 12
    due_year = year + ((month + 6) // 12)

    if due_year == 2016 and due_month > 3:
        return (2016,3)
    return (due_year, due_month)

def get_period(now, due):
    due_year, due_month = due
    now_year, now_month = now
    if now_year == due_year:
        return due_month - now_month
    elif due_month == 12:
        return 6
    else:
        return (12-now_month) + due_month

def payout_due(deposit, rate, period=6):
    # interest formula - assume monthly compounding for period months
    # default assumes 6 month cd
    return deposit * ((1 + rate/12.0) ** period)

def load_data():
    rate_dict = {}
    with open('cdrate.csv', 'r') as fd:
        reader = csv.reader(fd)
        for entry in reader:
            year, month = entry[0].partition('-')[::2]
            time = (int(year), int(month))
            rate = float(entry[1])/100
            rate_dict[time] = rate
    return rate_dict

def lifetime():
    rate_dict = load_data()
    due_dict = {}
    for year in range(1964,2017):
        for month in range(1,13):
            if year == 1964 and month < 6: continue
            if year == 2016 and month > 2: continue
            time = (year, month)
            if time in due_dict:
                base = due_dict.pop(time)
            else:
                base = 0

            addition = get_n_days(*time)

            due_on = due_month(*time)
            period = get_period(time, due_on)
            payout = payout_due(base+addition, rate_dict[time], period)
            print "creating a {} month cd in {} for {}, expecting {} on {}".format(period, time, base+addition, payout, due_on)

            due_dict.setdefault(due_on, 0.0)
            due_dict[due_on] += payout

    return due_dict
if __name__ == '__main__':
    print "Total value:", lifetime().values()[0] + get_n_days(2016, 3)

cdrate.csv