Week 15 Quiz

Predict, then check: what does this program print?

class Counter:
    def __init__(self):
        self.count = 0

    def increment(self):
        self.count = self.count + 1

c1 = Counter()
c2 = Counter()
c1.increment()
c1.increment()
c2.increment()
print(c1.count, c2.count)

Select one.

• 3 3
• 2 1
• 1 1
• 2 2

Predict, then check: what are the two lines this program prints?

class ReadingLog:
    def __init__(self, goal):
        self.goal = goal
        self.pages_read = 0

    def add_day(self, pages):
        self.pages_read = self.pages_read + pages

    def pages_left(self):
        return self.goal - self.pages_read

mine = ReadingLog(300)
yours = ReadingLog(150)
mine.add_day(45)
mine.add_day(30)
yours.add_day(45)
print(mine.pages_read, mine.pages_left())
print(yours.pages_read, yours.pages_left())

Select one.

• 75 225, then 120 30
• 45 255, then 45 105
• 75 225, then 45 105
• 75 225, then 75 75

This program never writes __init__ as a call. How many times does the line inside __init__ print, and why?

class ReadingLog:
    def __init__(self, goal):
        print("building a log with goal", goal)
        self.goal = goal
        self.pages_read = 0

mine = ReadingLog(300)
yours = ReadingLog(150)
print(mine.goal, yours.goal)

Select one.

• Twice, because each call to the class runs __init__ on the new object
• Never, because a method runs only when its name is called
• Once, when Python reads the class definition
• Three times, once for each line that names mine or yours

Which exception type ends this program?

class ReadingLog:
    def __init__(self, goal):
        self.goal = goal
        self.pages_read = 0

    def add_day(self, pages):
        self.pages_read = self.pages_read + pages

    def pages_left(self):
        return self.goal - self.pages_read

mine = ReadingLog(300)
mine.add_day(mine, 45)
print(mine.pages_read)

Select one.

• AttributeError
• NameError
• ValueError
• TypeError

Which exception type ends this program, the pinned missing-self example?

class Cat:
    def __init__(self, name):
        name = name

    def speak(self):
        return self.name + " says Meow"

c = Cat("Milo")
print(c.speak())

Select one.

• TypeError
• AttributeError
• NameError
• SyntaxError

Predict, then check: what are the two lines this program prints?

class ReadingLog:
    def __init__(self, goal):
        self.goal = goal
        self.pages_read = 0

    def add_day(self, pages):
        self.pages_read = self.pages_read + pages

    def pages_left(self):
        return self.goal - self.pages_read

    def report(self):
        print(self.pages_read, "of", self.goal)

mine = ReadingLog(300)
mine.add_day(45)
result = mine.report()
print(result)

Select one.

• 45 of 300, then None
• 45 of 300, then 45 of 300
• 45 of 300, then 255
• None, then 45 of 300

Which exception type ends this program?

class ReadingLog:
    def __init__(self, goal):
        self.goal = goal
        self.pages_read = 0

    def add_day(self, pages):
        self.pages_read = self.pages_read + pages

    def pages_left(self):
        return self.goal - self.pages_read

mine = ReadingLog(300)
add_day(45)

Select one.

• TypeError
• AttributeError
• NameError
• It adds 45 to mine and prints nothing

Predict, then check: what does this program print?

class ReadingLog:
    def __init__(self, goal):
        self.goal = goal
        self.pages_read = 0

    def add_day(self, pages):
        self.pages_read = self.pages_read + pages

    def pages_left(self):
        return self.goal - self.pages_read

mine = ReadingLog(300)
mine.add_day(45)
same = mine
same.add_day(30)
print(mine.pages_read, same is mine)

Select one.

• 45 False
• 30 False
• 75 False
• 75 True

Predict, then check: what does this program print?

class ReadingLog:
    def __init__(self, goal):
        self.goal = goal
        self.pages_read = 0

    def add_day(self, pages):
        pages_read = self.pages_read + pages

mine = ReadingLog(300)
mine.add_day(45)
print(mine.pages_read)

Select one.

• 45
• 0
• AttributeError
• None

True or false: in the method header def add_day(self, pages):, the call mine.add_day(45) hands mine to self automatically, so the caller writes only the 45.

True or false.

• True
• False