Unit 3: OOP concepts - Practice Quiz

1 What is a class in Python?

2 What is an object in object-oriented programming?

3 Which special method commonly initializes a new Python object?

4 What does the self parameter represent in an instance method?

5 What is a method in a Python class?

6 Which OOP feature allows one interface to support different behaviors?

7 Which OOP feature focuses on showing essential behavior while hiding implementation details?

8 What is encapsulation in object-oriented programming?

9 Which Python naming style indicates that an attribute is intended for internal use?

10 What happens to an instance attribute named __balance inside a Python class?

11 What is the usual purpose of a getter method?

12 What is the usual purpose of a setter method?

13 Which Python feature can provide controlled access to an attribute using method-like logic?

14 Which built-in decorator is commonly used to define a property getter?

15 What does inheritance allow a Python class to do?

16 In class Dog(Animal):, which class is the parent class?

17 In class Dog(Animal):, which class is the child class?

18 Which function is commonly used to access a parent class implementation?

19 What is method overriding?

20 What is multiple inheritance in Python?

21 What is printed by the following code?

class Wallet:
    def __init__(self, amount):
        self.amount = amount

    def add(self, value):
        self.amount += value

w1 = Wallet(100)
w2 = Wallet(100)
w1.add(50)
print(w1.amount, w2.amount)

22 What is the output of this polymorphic code?

class Dog:
    def speak(self):
        return 'Woof'

class Cat:
    def speak(self):
        return 'Meow'

animals = [Dog(), Cat()]
print([animal.speak() for animal in animals])

23 A Car object creates and stores an Engine object as self.engine. Which OOP relationship does this primarily represent?

24 What is printed by the following code?

class Counter:
    total = 0

    def __init__(self):
        Counter.total += 1

c1 = Counter()
c2 = Counter()
c1.total = 10
print(c1.total, c2.total, Counter.total)

25 Which method should be implemented so that print(book) displays a student-friendly description of a Book object?

26 A function calls shape.area() on objects from unrelated classes without checking their types. Which Python OOP feature makes this design practical?

27 What happens when this code executes?

from abc import ABC, abstractmethod

class Report(ABC):
    @abstractmethod
    def generate(self):
        pass

class SalesReport(Report):
    pass

r = SalesReport()

28 What happens when the final statement executes?

class Account:
    def __init__(self):
        self.__balance = 500

a = Account()
print(a.__balance)

29 What is the result of assigning p.price = -20?

class Product:
    def __init__(self, price):
        self._price = price

    @property
    def price(self):
        return self._price

    @price.setter
    def price(self, value):
        if value < 0:
            raise ValueError('Invalid price')
        self._price = value

p = Product(50)
p.price = -20

30 What does a single leading underscore in an attribute such as self._score indicate in Python?

31 What happens at the final statement?

class Temperature:
    def __init__(self, value):
        self._value = value

    @property
    def value(self):
        return self._value

t = Temperature(25)
t.value = 30

32 What is printed by this code?

class Config:
    __mode = 'safe'

    @classmethod
    def get_mode(cls):
        return cls.__mode

print(Config.get_mode(), hasattr(Config, '__mode'))

33 What does the following code print?

class Base:
    def __value(self):
        return 'Base'

    def show(self):
        return self.__value()

class Child(Base):
    def __value(self):
        return 'Child'

print(Child().show())

34 What is printed by the final statement?

class Cart:
    def __init__(self):
        self.__items = []

    @property
    def items(self):
        return self.__items.copy()

cart = Cart()
view = cart.items
view.append('pen')
print(cart.items)

35 What is printed by this code?

class Person:
    def __init__(self, name):
        self.name = name

class Student(Person):
    def __init__(self, name, grade):
        super().__init__(name)
        self.grade = grade

s = Student('Asha', 9)
print(s.name, s.grade)

36 What does this overridden method return?

class Parent:
    def message(self):
        return 'P'

class Child(Parent):
    def message(self):
        return super().message() + 'C'

print(Child().message())

37 What is printed according to Python's method resolution order?

class A:
    def run(self):
        print('A', end=' ')

class B(A):
    def run(self):
        print('B', end=' ')
        super().run()

class C(A):
    def run(self):
        print('C', end=' ')
        super().run()

class D(B, C):
    pass

D().run()

38 What is printed by the following code?

class Base:
    rate = 5

class Child(Base):
    pass

c1 = Child()
c2 = Child()
c1.rate = 8
print(c2.rate, Base.rate)

39 What does this code print?

class Base:
    pass

class Child(Base):
    pass

obj = Child()
print(isinstance(obj, Child), isinstance(obj, Base), type(obj) is Base)

40 What is printed by the following code?

class Base:
    def greet(self):
        return 'Base'

class Child(Base):
    def greet(self):
        return 'Child'

c = Child()
print(c.greet(), super(Child, c).greet())

41 What does the following code print?

class A:
    items = []

    def add(self, value):
        self.items += [value]

a = A()
b = A()
a.add(1)
print(A.items, b.items, a.items is b.items)

42 What does the following code print?

class A:
    def __f(self):
        return "A"

    def call(self):
        return self.__f()

class B(A):
    def __f(self):
        return "B"

print(B().call())

43 What is printed when both a base class and its subclass declare a private slot with the same source-level name?

class A:
    __slots__ = ("__x",)

    def __init__(self):
        self.__x = 1

    def from_a(self):
        return self.__x

class B(A):
    __slots__ = ("__x",)

    def __init__(self):
        super().__init__()
        self.__x = 2

    def from_b(self):
        return self.__x

b = B()
print(b.from_a(), b.from_b())

44 What does this code print?

class C:
    @property
    def x(self):
        return 10

c = C()
c.__dict__["x"] = 99
print(c.x, c.__dict__["x"])

45 What is the result of this managed attribute lookup?

class C:
    @property
    def x(self):
        raise AttributeError("hidden")

    def __getattr__(self, name):
        return f"fallback:{name}"

print(C().x)

46 What does the following code print?

class Base:
    @property
    def x(self):
        return 1

class Child(Base):
    x = 5

c = Child()
c.x = 9
print(c.x)

47 What does Python print for this cooperative diamond hierarchy?

class A:
    def f(self):
        return "A"

class B(A):
    def f(self):
        return "B" + super().f()

class C(A):
    def f(self):
        return "C" + super().f()

class D(B, C):
    def f(self):
        return "D" + super().f()

print(D().f())

48 What is the final trace produced by these cooperative initializers?

class A:
    def __init__(self, **kwargs):
        self.trace = ["A"]
        super().__init__(**kwargs)

class B(A):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.trace.append("B")

class C(A):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.trace.append("C")

class D(B, C):
    def __init__(self):
        super().__init__()
        self.trace.append("D")

print(D().trace)

49 At which statement does Python first raise an exception?

class X:
    pass

class Y:
    pass

class A(X, Y):
    pass

class B(Y, X):
    pass

class C(A, B):
    pass

50 What does this class-method call return?

class A:
    @classmethod
    def who(cls):
        return cls.__name__

class B(A):
    @classmethod
    def who(cls):
        return super().who() + ":B"

print(B.who())

51 What happens in this abstract-base-class example?

from abc import ABC, abstractmethod

class A(ABC):
    @abstractmethod
    def f(self):
        return "A"

class B(A):
    def f(self):
        return super().f() + "B"

print(B().f())

52 Which result correctly describes this virtual subclass registration?

from abc import ABC, abstractmethod

class Protocol(ABC):
    @abstractmethod
    def run(self):
        pass

class Worker:
    pass

Protocol.register(Worker)
w = Worker()

53 What does this code print after mutation through one subclass and rebinding through another?

class A:
    data = []

class B(A):
    pass

class C(A):
    pass

B.data.append(1)
C.data = C.data + [2]
print(A.data, B.data, C.data)

54 Which special method handles the following addition?

class A:
    def __add__(self, other):
        return "A.__add__"

class B(A):
    def __radd__(self, other):
        return "B.__radd__"

print(A() + B())

55 What happens when hash(B()) is evaluated?

class A:
    def __hash__(self):
        return 7

class B(A):
    def __eq__(self, other):
        return True

56 What does this code print?

class C:
    def __len__(self):
        return 3

c = C()
c.__len__ = lambda: 9
print(len(c), c.__len__())

57 What is printed by this singleton-style implementation?

class C:
    _one = None

    def __new__(cls):
        if cls._one is None:
            cls._one = super().__new__(cls)
        return cls._one

    def __init__(self):
        self.n = getattr(self, "n", 0) + 1

a = C()
b = C()
print(a is b, a.n)

58 After executing the setup below, which expression raises TypeError?

class C:
    def f(self, x):
        return x

c = C()
c.g = C.f

59 What happens when the copied method is called?

class A:
    def ping(self):
        return "A"

class B(A):
    def ping(self):
        return super().ping() + "B"

class C(A):
    ping = B.ping

print(C().ping())

60 What does this descriptor example print?

class Label:
    def __get__(self, obj, owner):
        return "descriptor"

class C:
    x = Label()

c = C()
c.x = "instance"
print(c.x)