be-a-computer.md

Be-a-Computer: Classes and Objects

In the following exercises, you will be shown a piece of code, and will have to figure out what it does (without running it yourself in the Python interpreter)

Exercise #1

Given the following class definition:

class Mystery:
    def __init__(self, v0, v1):
        self._v0 = v0
        self._v1 = v1

    def get_a(self):
        return self._v0+1

    def get_b(self):
        return self._v1*2

    def get_c(self):
        return self.get_a() + self.get_b()

    def do_d(self, val):
        self._v0, self._v1 = val

    def __str__(self):
        return str((self.get_a(), self.get_b(), self.get_c()))

What is the output of the following code?

m0 = Mystery(1, 2)
m0.do_d((m0.get_a(), m0.get_c()))
print(m0)

m1 = Mystery(3, 4)
m1.do_d((m0.get_a(), m1.get_b()))
print(m1)

Exercise #2

This exercise uses the following constants and data:

(DATE, TICKER, OPEN, CLOSE) = (0, 1, 2, 3)

stocks = [['Date', 'Ticker Symbol', 'Open', 'Close'],
        ['2010-11-09', 'AMD', '8.22', '7.91'],
        ['2010-11-09', 'GOOG', '630.00', '624.82'],
        ['2010-11-09', 'QQQ', '53.95', '54.26'],
        ['2010-11-10', 'AMD', '8.22', '8.72'],
        ['2010-11-10', 'BSB', '620.00', '630.40'],
        ['2010-11-10', 'GOOG', '630.00', '630.40'],
        ['2010-11-10', 'QQQ', '53.95', '53.45'],
        ['2010-11-11', 'AMD', '8.22', '8.40'],
        ['2010-11-11', 'GOOG', '630.00', '634.82'],
        ['2010-11-11', 'QQQ', '53.95', '53.45']]

What is the output of the following code?

class Stock_Info(object):
    def __init__(self, date, ticker, opening_price, closing_price):
        self.date = date
        self.ticker = ticker
        self.opening_price = opening_price
        self.__closing_price = closing_price

    def get_closing_price(self):
        return self.__closing_price

    def set_closing_price(self, correct_value):
        self.__closing_price = correct_value

    def __repr__(self):
        return "|".join([self.date, self.ticker, 
                        self.opening_price, self.__closing_price])


def create_dict(data):
    rv = {}
    for row in data:
        tkr = row[TICKER]
        s = Stock_Info(row[DATE], tkr, row[OPEN], row[CLOSE])
        if tkr not in rv:
            rv[tkr] = []
        rv[tkr].append(s)

    return rv
        
def mystery(d, list0):
    for (x, y, z) in list0:
        for a in d[x]:
            if a.date == y:
                a.set_closing_price(z)
                break


d = create_dict(stocks)
entries = [["GOOG", '2010-11-09', '625.00'], 
           ['GOOG', '2010-11-10', '634.82']]
mystery(d, entries)
for s in d["GOOG"]:
    print(s)