Be-A-Computer: Classes and Objects¶
The purpose of these problems is to allow you to test your understanding of classes and objects. They should not take more than an hour to complete.
You should do these warm-up exercises by hand. We provide files that will allow you to check your answers.
To get started, run git pull upstream master
to make
sure you have the latest files. You can check your answers by
running the code provided in pp/bac/
Warm-up 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 result of evaluating 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)
You can find the code for this example in pp/bac/classes_1.py.
Warm-up exercise #2:¶
This warm-up 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)
You can find the code for this example in pp/bac/classes_2.py.