Peer Instruction: Inheritance Multiple Choice Questions

Q-1: In the following pairs of words, the first is the subclass and the second is the superclass. Which of them is a correct example of inheritance?

• dog, cat
• Incorrect! A Dog is not a Cat.
• dog, animal
• Correct! A Dog is an Animal where Dog is the subclass and Animal is the superclass.
• animal, dog
• Incorrect! A Dog is an Animal where Dog is the subclass and Animal is the superclass and not the other way around.
• dog, tail
• Incorrect! A Dog has a Tail. It's not a "is-a" relationship.
• None of the above
• Incorrect! A Dog is an Animal where Dog is the subclass and Animal is the superclass.

Q-2: What is the output of this code?

class A:
   def __init__(self, x):
      self.x = x
   def __str__(self):
      return str(self.x)

class B(A):
   def __init__(self, x):
      self.x = x * 2

b = B(5)
print(b)

• 5
• Incorrect! A Subclass only specifies what is different from its Superclass. Here B is the subclass and A is the superclass where only the "__init__" method is different them. Since "b = B(5)" has been called, the "__init__" method from B will be executed and not A. So, "x=5" will be multuplied by 2.
• 10
• Correct! A Subclass only specifies what is different from its Superclass. Here B is the subclass and A is the superclass where only the "__init__" method is different them. Since "b = B(5)" has been called, the "__init__" method from B will be executed and not A. So, "x=5" will be multuplied by 2.
• 510
• Incorrect! A Subclass only specifies what is different from its Superclass. Here B is the subclass and A is the superclass where only the "__init__" method is different them. Since "b = B(5)" has been called, the "__init__" method from B will be executed and not A. So, "x=5" will be multuplied by 2.
• This will cause an error
• Incorrect! This will not cause an error. A Subclass only specifies what is different from its Superclass. Here B is the subclass and A is the superclass where only the "__init__" method is different them. Since "b = B(5)" has been called, the "__init__" method from B will be executed and not A. So, "x=5" will be multuplied by 2.
• I don't know
• Incorrect! A Subclass only specifies what is different from its Superclass. Here B is the subclass and A is the superclass where only the "__init__" method is different them. Since "b = B(5)" has been called, the "__init__" method from B will be executed and not A. So, "x=5" will be multuplied by 2.

Q-3: What is the output of this code?

class Person:

   count = 0

   def __init__(self,first="J",last="Doe"):
     self.first = first
     self.last = last
     Person.count = Person.count + 1

   def __str__(self):
     return self.first + " " + self.last

   def work(self):
     print("Gotta pay the bills")

   def play(self):
     print("TV time!")

   def eat(self):
     print("Woohoo, fast food!")

   def sleep(self):
     print("Zzzzzzzzzzzzzzzz")

class Student(Person):

   def __init__(self,first,last,year):
     Person.__init__(self,first,last)
     self.year = year

   def sleep(self):
     print("So tired.... but... Internet!")

   def study(self):
     print("Need to study... but... Internet!")

   def __str__(self):
     return Person.__str__(self)+" '"+str(self.year%100)


p = Person(“George”, “Williker”)
s = Student(“Buddy”,”Bob”, "2014")
s.study()
p.study()

• "Need to study...but...Internet!” will print twice
• Incorrect! There's a "study" attribute in Student but not in Person.
• "Need to study... but...Internet!” will print once
• Correct! There's a "study" attribute in Student but not in Person.
• Nothing will print
• Incorrect! There's a "study" attribute in Student but not in Person.
• This will cause an error
• Incorrect! There's a "study" attribute in Student but not in Person.
• I don't know
• Incorrect! There's a "study" attribute in Student but not in Person.

Q-4: What is the output of this code?

class A:
   count = 0
   def __init__(self, x):
      self.x = x+1
      A.count = A.count+1

A1 = A(2)
A2 = A(4)
A3 = A(5)

print(A1.x, A1.count, A.count)

• 3, 1, 1
• Incorrect! Here "count" is a class variable which is shared by all objects of type A. It can be accessed by using A.count, A1.count, A2.count, and A3.count. "self.x" is unique for each object. So, "A1.x = 2 + 1 = 3" whereas "count" gets added by "1" thrice.
• 3, 1, 3
• Incorrect! Here "count" is a class variable which is shared by all objects of type A. It can be accessed by using A.count, A1.count, A2.count, and A3.count. "self.x" is unique for each object. So, "A1.x = 2 + 1 = 3" whereas "count" gets added by "1" thrice.
• 3, 3, 3
• Correct! Here "count" is a class variable which is shared by all objects of type A. It can be accessed by using A.count, A1.count, A2.count, and A3.count. "self.x" is unique for each object. So, "A1.x = 2 + 1 = 3" whereas "count" gets added by "1" thrice.
• 2, 1, 1
• Incorrect! Here "count" is a class variable which is shared by all objects of type A. It can be accessed by using A.count, A1.count, A2.count, and A3.count. "self.x" is unique for each object. So, "A1.x = 2 + 1 = 3" whereas "count" gets added by "1" thrice.
• I don't know
• Incorrect! Here "count" is a class variable which is shared by all objects of type A. It can be accessed by using A.count, A1.count, A2.count, and A3.count. "self.x" is unique for each object. So, "A1.x = 2 + 1 = 3" whereas "count" gets added by "1" thrice.

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