PyLab and Mortgage Example

It has been a long time since I made a post.  I have a lot of things going on and really only have time to post when I am not too busy.

In this post, I am working with Guttag's mortgage example for PyLab.   This comes from chapter 11 of his book. The example compares 3 different mortgages. Here are the charts I created using Pylab:

The charts are saved in he  format.  To see the the example, please see Guttag's book on Python. 

The question is- as always- is Pylab easy to work with for making graphs?  This depends.  I know a lot of people who find it easier to make graphs in R or Tableau. They also like the quality of the graphs in R and Tableau.  In Python, making graphs is not as easy as R or Tableau but the formers are both functional programs, while Python is a general programming language.


Here is some of the code for the charts:


def findPayment(loan, r, m):
    """ Assumes: loan and r are floats, m an int
        Returns the monthly payment for a mortgage of size
        loan at a monthly rate of r for m months """
    return loan*((r*(1+r)**m)/((1 + r)**m - 1))

class Mortgage(object):
    """ Abstract class for building different kinds of mortgages """
    def __init__(self, loan, annRate, months):
        self.loan = loan
        self.rate = annRate/12.0
        self.months = months
        self.paid = [0.0]
        self.outstanding = [loan]
        self.payment = findPayment(loan, self.rate, months)
        self.legend = None #description of mortgage

def plotMortgages(morts, amt):

    def labelPlot(figure, title, xLabel, yLabel):

        pylab.figure(figure)

        pylab.title(title)

        pylab.xlabel(xLabel)

        pylab.ylabel(yLabel)

        pylab.legend(loc = 'best')

    styles = ['k-', 'k-.', 'k:']

    # give names to figure numbers

    payments, cost, balance, netCost = 0,1,2,3

    for i in range(len(morts)):

        pylab.figure(payments)

        morts[i].plotPayments(styles[i])

        pylab.figure(cost)

        morts[i].plotTotPd(styles[i])

        pylab.figure(balance)

        morts[i].plotBalance(styles[i])

        pylab.figure(netCost)

        morts[i].plotNet(styles[i])

    labelPlot(payments, 'Monthly Payments of $' + str(amt) + ' Mortgages', 'Months', 'Monthly Payments')

    labelPlot(cost, 'Cash Outlay of $' + str(amt) + ' Mortgages', 'Months', 'Total Payments')

    labelPlot(balance, 'Balance Remaining of $' + str(amt) + 'Mortgages', 'Months', 'Remaining Loan Balance of $')

    labelPlot(netCost, 'Net Cost of $' + str(amt) + ' Mortgages', 'Months', 'Payments - Equity $')

    

def compareMortgages(amt, years, fixedRate, pts, ptsRate, varRate1, varRate2, varMonths):

        totMonths = years*12

        fixed1 = Fixed(amt, fixedRate, totMonths)

        fixed2 = FixedWithPts(amt, ptsRate, totMonths, pts)

        twoRate = TwoRate(amt, varRate2, totMonths, varRate1, varMonths)

        morts = [fixed1, fixed2, twoRate]

        for m in range(totMonths):

            for mort in morts:

                mort.makePayment()

        plotMortgages(morts, amt)

        pylab.show()

compareMortgages(amt=200000, years = 30, fixedRate = 0.07, pts = 3.25,

                 ptsRate = 0.05, varRate1 = 0.045, varRate2 = 0.095,

                 varMonths= 48)