npvtools.py

"""
npvtools.py
Spring 2020 PJW

Module providing functions for computing NPVs of cashflows
stored in text files.
"""

#
#  Read a cashflow file and return a list of dated payments
#

def read_cashflow(filename,splitter=None):
    pmts = []
    fh = open(filename)
    for line in fh:
        words = line.split(splitter)
        new_pmt = { 't':int(words[0]), 'amt':float(words[1]) }
        pmts.append(new_pmt)
    fh.close()
    return pmts

#
#  Given an interest rate and a list of dated payments, compute
#  an NPV.
#

def npv(r,cashflow):
    val = 0
    for pmt in cashflow:
        val = val + pmt['amt']/(1+r)**pmt['t']
    return val