[Tutor] printing puzzlement

[Danny Yoo]

On Fri, 9 Aug 2002, Rob wrote:

> As seen in the C++ code snippet here, calculations are performed in the
> middle of the display of each line of output.

Yikes.  It's usually not a good thing when "presentation logic" --- the
table display --- is so closely tied to the calculation logic.  Perhaps we
can try to refactor this, and yank out the calculation into separate
functions.



> 	cout <<	"Pmt #  Cur. Prin.  Payment  Int. Paid  Rem. Prin." << endl;
> 	cout <<
> 		"-----  ----------  -------  ---------  ----------" << endl;
> 	for (int index = 0; index < numPayments; index++)
> 	{
> 		cout << setw(5) << right << (index + 1);
> 		cout << setw(12) << right << fixed
>                    << setprecision(2) << principle;
> 		cout << setw(9) << right << fixed << amtPayment;
> 		float interest =
>                   (float (int (principle * monthRate * 100) ) ) / 100.0;
> 		cout << setw(11) << right << fixed << interest;
> 		principle = principle + interest - amtPayment;
> 		cout << setw(12) << right << fixed << principle;
> 		cout << endl;
> 	}


Here's one possible way to recode this:


###
## Warning: untested code

class AmortizationSchedulePrinter:

    def __init__(self, starting_principle, amtPayment, monthRate):
        self.startingPrinciple = startingPrinciple
        self.amtPayment = amtPayment
        self.monthRate = monthRate


    def printAmortizationSchedule(self):
        self.printHeader()
        p = self.startingPrinciple
        for index in range(self.numPayments):
            printReportLine(index, p)
            p = self.nextPrinciple(p)


    def printReportLine(self, index, principle):
        print ("%5f"
               "%12.2f"
               "%9.2f"
               "%11.2f"
               "%12.2f") % \
              (index + 1,
               principle,
               self.amtPayment,
               self.interest(principle),
               self.nextPrinciple(principle))


    def nextPrinciple(self, principle):
        return principle + self.interest(principle) - self.amtPayment;


    def interest(self, principle):
        return (float (int (principle * self.monthRate * 100) ) ) / 100.0;


    def printHeader(self):
        print "Pmt #  Cur. Prin.  Payment  Int. Paid  Rem. Prin."
        print "-----  ----------  -------  ---------  ----------"
###


It is a bit longer than the original version, but it does allow us to make
changes to the line format more easily, since all of the formatting stuff
is in printHeader() and printReportLine().


Hope this helps!