19.14. Multiple Choice Questions

Q-1: Which of the following does not correctly create an object instance?

• student = Person("Charles")
• This uses a constructor to initialize object attributes. Try again.
• person = Person("Charles")
• This uses a constructor to initialize object attributes. The instance can have a similar name to the class. Try again.
• Charles = Person()
• This is correct and does not have arguments. Try again.
• student = new Person("Charles")
• Correct! 'new' is incorrect.

Q-2: Which of the following is the correct way to define a constuctor (intializer)?

• def __init__(title, author):
• Incorrect! Unless a class method is static, 'self' is needed to represent the current instance. Try again.
• def __init__(self, title, author):
• Correct! The "self" is used to represent an instance of the given class and the parameters will be used to initialize attributes.
• def __init__():
• Incorrect! At minimum, the "self" parameter is needed to represent an instance of the given class. Try again.
• def init(self, title, author):
• Incorrect! The method name is __init__. Try again.

Q-3: How many attributes does an object of the Book class have?

class Book:

  def __init__(self, title, author, pages, price, age_group):
    self.title = title
    self.author = author
    self.pages = pages
    self.price = price
    self.age_group = age_group

  def __str__(self):
    return "title: " + self.title + " author: " + self.author + " pages: " + self.pages + " price: " + self.price + " age_group: " + self.age_group

• 2
• Incorrect! This is the number of methods in the Book Class. Try again.
• 3
• Incorrect! How many items are initialized in the __init__ method?
• 6
• Incorrect! We do not count the 'self' as an attribute. Try again.
• 5
• Correct! There are five attributes that are initialized in the __init__ method.

Q-4: What should be in the underlined section in the getX method of the Point class?

class Point:

  def __init__(self, initX, initY):
    self.x = initX
    self.y = initY

  def getX(self):
    return ______

• x
• Incorrect! We need to refer to the current instance of the class. Try again.
• print(x)
• Incorrect! We do not want print a value. We want to return the attribute value. Try again.
• self.x
• Correct! Here 'self' is used to represent the current instance of the class.
• init.x
• Incorrect! There is nothing like init.x since we are using the 'self' in the class. Try again.

Q-5: What does the following code output?

class Person():

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

    def __str__(self):
      print("Name: " + self.name)

  person1 = Person("James")
  person2 = Person("Tony")
  print(person1)

• Name: James
• Correct! This prints the string returned from the __str__ method.
• Name: Tony
• Incorrect! 'Tony' is the 'name' of person2 but we are printing the person1 instance. Try again.
• Name: James Name: Tony
• Incorrect! It does not print both objects.
• person1
• Incorrect! The output is not the name of the instance. Try again.

Q-6: Which of the following statements is incorrect about the following code?

class Person():

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

  def __str__(self):
    print("Name: " + self.name)

person1 = Person("James")
person2 = Person("Tony")
print(person1)

• person1 and person2 are two different instances of the People class.
• Since two different objects were created, this is correct. Try again.
• The __init__ class is used to create instances and set initial values for its attributes.
• __init__ is an optional method in classes that is used to set initial values for objects. Try again.
• As we are not updating any values, 'self' does not need to be passed to the __str__ method.
• Correct! Here 'self' is used to represent the current instance of the class and the current object must be passed into the __str__ method.
• person2 cannot access the 'name' of person1.
• Since they are two different instances, they cannot access each other and have different initial values too. Try again.

Q-7: Which of the following statements is not true about object-oriented programming?

• One of the benefits of object-oriented programming is that it can hide complexity.
• This is true, while using an object, we need to know how to use the object, but not how it works internally. Try again.
• A class defines a number of functions as well as the data that is used by those functions.
• This is true as a class defines functions as well as data that is used by those functions. Try again.
• Constructor methods are required to initialize an object and destructor methods are required to destroy the object when no longer required.
• Correct! This is false, a constructor is optional can be used to set initial values for an object and python automatically destroys any object if its reference count changes to a zero without needing a destructor.
• The __str__ method is responsible for returning a string representation for an object.
• This is true, we can print information about an object with the __str__ method. Try again.

Q-8: Which of the following is the correct way to define the __str__ method which returns a string with the title and author?

• def __str__(title, author):
• Incorrect! Unless a class method is static, 'self' is used to represent the current instance. Try again.
• def __str__(self):
• Correct! The "self" is used to represent an instance of the given class.
• def __str__():
• Incorrect! The "self" parameter is needed to represent an instance of the given class. Try again.
• def str(self):
• Incorrect! The method is __str__. Try again.

Q-9: The _________ keyword defines a template for objects of a class.

• Class
• Incorrect! Python is case sensitive. It should be class not Class.
• object
• Incorrect! An object is created by a class. Try again.
• class
• Correct! The keyword is class.
• instance
• Incorrect! An instance is created from a class. Try again.

Q-10: _________ is by convention used to represent the current instance of a class and to access the attributes and methods of the class.

• class
• Incorrect! The 'class' keyword defines a template for all objects of the class. Try again.
• def
• Incorrect! The 'def' keyword defines a function. Try again.
• self
• Correct! While 'self' is not a keyword, the convention is to use it to represent the current object.
• init
• Incorrect! The 'init' is not a keyword, but the __init__ method is created to initialize object attributes. Try again.

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