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Python for Everyone: The PreTeXt Interactive Edition

Exercises 19.14 Multiple Choice Questions

1.

    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.

2.

    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.

3.

    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.

4.

    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.

5.

    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.

6.

    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.

7.

    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.

8.

    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.

9.

    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.

10.

    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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