Quiz 6a#

Question 1#

Every class definition should include an initializer method. What is the name of the initializer method?

Refer to the first object-oriented programming video.

Note : While you can get away with not having an initializer method, doing so almost always implies using techniques beyond the scope of this course or bad program design. So, beginners should always define an initializer method.

The same as the name of the class
init
__init__ (2 underscores on each side)
_init_ (1 underscore on each side) \

__init__ (2 underscores on each side)

Question 2#

In Python, what is the main difference between a function and a method ?

Methods have a parameter named self, while functions do not.
There is no difference. They are interchangeable terms.
Methods are defined in built-in library modules, while functions are defined in your own code.
Functions are defined outside of classes, while methods are defined inside of and part of classes. \

Functions are defined outside of classes, while methods are defined inside of and part of classes. \

Question 3#

As an example class, consider the following code from one of the videos:

class Character:
    def __init__(self, name, initial_health):
        self.name = name
        self.health = initial_health
        self.inventory = []
        
    def __str__(self):
        s += "Name: " + self.name
        s += " Health: " + str(self.health)
        s += " Inventory: " + str(self.inventory)
        return s
    
    def grab(self, item):
        self.inventory.append(item)
        
    def get_health(self):
        return self.health

What does the self parameter represent?

The method that is being defined
An object (instance) of the Character class
The Character class
Whatever happens to be passed to it. \

An object (instance) of the Character class \

Question 4#

Assume you have the following class and method definition, parts of which have been omitted.

class My_Class:
    #…

    def my_method(self, value1, value2):
        """Assumes its inputs are two values and does something."""
        #…

my_object = My_Class()

The last line defines the variable my_object as an object of My_Class class. Which of the following is proper syntax for using the method on this object?

my_method(My_Class, 1, 2)
My_Class.my_method(my_object, 1, 2)
my_object.my_method(1, 2)
My_Class.my_object.my_method(1, 2)
my_method(my_object, 1, 2) \

my_object.my_method(1, 2) \

Note that even My_Class.my_method(my_object, 1, 2) has the same behavior, it is not the proper way of using the method.

Question 5#

We want to have balls that move around. Which of the following designs represents encapsulation best?

  class Ball:
    def __init__(self, c, r):
        self.center = c
        self.radius = r

    def get_position(self):
        return self.center

    def set_position(self, new_position):
        self.center = new_position

# balls : A list of Ball objects
balls = #…

def move(ball, move_vector):
    """
    Changes the position of the ball by the given vector.
    """
    position = ball.get_position()
    position[0] += move_vector[0]
    position[1] += move_vector[1]
    ball.set_position(position)
 

  class Ball:
    def __init__(self, c, r):
        self.center = c
        self.radius = r

    def move(self, move_vector):
        """
        Changes the position of the ball by the given vector.
        """
        self.center[0] += move_vector[0]
        self.center[1] += move_vector[1]

# balls : A list of Ball objects
balls = #…
 

  class Ball:
    def __init__(self, c, r):
        self.center = c
        self.radius = r

# balls : A list of Ball objects
balls = #…

def move(ball, move_vector):
    """
    Changes the position of the ball by the given vector.
    """
    ball.center[0] += move_vector[0]
    ball.center[1] += move_vector[1]
 

  # centers : A list of points, the balls' center points
centers = #…

# radii : A list of numbers, the balls' radii
radii = #…

def move(ball_number, move_vector):
    """
    Changes the position of the ball by the given vector.
    """
    centers[ball_number][0] += move_vector[0]
    centers[ball_number][1] += move_vector[1]
 

  class Ball:
    def __init__(self, c, r):
        self.center = c
        self.radius = r

    def move(self, move_vector):
        """
        Changes the position of the ball by the given vector.
        """
        self.center[0] += move_vector[0]
        self.center[1] += move_vector[1]

# balls : A list of Ball objects
balls = #…
 

Other choices do not integrate move() into the Ball class.

Question 6#

A common feature in many object-oriented languages is method overloading . In this quiz question, you will learn by example what overloading is and whether or not Python supports it.

Turn the following English description into code.

- Start a class definition. We’ll call the class Overload.
- Define an init method. Along with the standard self it has one parameter. The method does nothing useful for this example — use the Python do-nothing statement pass for the body.
- Define a second init method. Along with self it has two parameters. This method also does nothing useful.

Outside of the class, we want to create two Overload objects. If Python supports overloading, you will be able to create an Overload object with one argument, and create another Overload object with two arguments. Does Python support overloading?

No
Yes \

No. The second method overwrites the first one.

class Overload:
    def __init__(self, p1):
        pass

    def __init__(self, p1, p2):
        pass


o = Overload(1)
o = Overload(1, 2)

Question 7#

First, complete the following class definition:

class BankAccount:
    def __init__(self, initial_balance):
        """Creates an account with the given balance."""
        #…

    def deposit(self, amount):
        """Deposits the amount into the account."""
        #… 

   def withdraw(self, amount):
        """
        Withdraws the amount from the account. Each withdrawal 
        resulting in a negative balance also deducts a penalty 
        fee of 5 dollars from the balance.
        """
        #…

    def get_balance(self):
        """Returns the current balance in the account."""
        #…

    def get_fees(self):
        """Returns the total fees ever deducted from the account."""
        #…

The deposit and withdraw methods each change the account balance. The withdraw method also deducts a fee of 5 dollars from the balance if the withdrawal (before any fees) results in a negative balance. Since we also have the method get_fees you will need to have a variable to keep track of the fees paid.

Here’s one possible test of the class. It should print the values 10 and 5, respectively, since the withdrawal incurs a fee of 5 dollars.

my_account = BankAccount(10)
my_account.withdraw(15)
my_account.deposit(20)
print my_account.get_balance(), my_account.get_fees()

Copy-and-paste the following much longer test. What two numbers are printed at the end? Enter the two numbers, separated only by spaces.

my_account = BankAccount(10)
my_account.withdraw(5)
my_account.deposit(10)
my_account.withdraw(5)
my_account.withdraw(15)
my_account.deposit(20)
my_account.withdraw(5)
my_account.deposit(10)
my_account.deposit(20)
my_account.withdraw(15)
my_account.deposit(30)
my_account.withdraw(10)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(50)
my_account.deposit(30)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(5)
my_account.deposit(20)
my_account.withdraw(15)
my_account.deposit(10)
my_account.deposit(30)
my_account.withdraw(25)
my_account.withdraw(5)
my_account.deposit(10)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(10)
my_account.withdraw(15)
my_account.deposit(10)
my_account.deposit(30)
my_account.withdraw(25)
my_account.withdraw(10)
my_account.deposit(20)
my_account.deposit(10)
my_account.withdraw(5)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(5)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(5)
print my_account.get_balance(), my_account.get_fees()

Enter answer here:\

-60 75

class BankAccount:
    def __init__(self, initial_balance):
        """Creates an account with the given balance."""
        self.balance = initial_balance
        self.fees = 0

    def deposit(self, amount):
        """Deposits the amount into the account."""
        self.balance += amount

    def withdraw(self, amount):
        """
        Withdraws the amount from the account. Each withdrawal
        resulting in a negative balance also deducts a penalty
        fee of 5 dollars from the balance.
        """
        self.balance -= amount
        if self.balance < 0:
            self.balance -= 5
            self.fees += 5

    def get_balance(self):
        """Returns the current balance in the account."""
        return self.balance

    def get_fees(self):
        """Returns the total fees ever deducted from the account."""
        return self.fees


# test
my_account = BankAccount(10)
my_account.withdraw(15)
my_account.deposit(20)
print(my_account.get_balance(), my_account.get_fees())


# actual
my_account = BankAccount(10)
my_account.withdraw(5)
my_account.deposit(10)
my_account.withdraw(5)
my_account.withdraw(15)
my_account.deposit(20)
my_account.withdraw(5)
my_account.deposit(10)
my_account.deposit(20)
my_account.withdraw(15)
my_account.deposit(30)
my_account.withdraw(10)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(50)
my_account.deposit(30)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(5)
my_account.deposit(20)
my_account.withdraw(15)
my_account.deposit(10)
my_account.deposit(30)
my_account.withdraw(25)
my_account.withdraw(5)
my_account.deposit(10)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(10)
my_account.withdraw(15)
my_account.deposit(10)
my_account.deposit(30)
my_account.withdraw(25)
my_account.withdraw(10)
my_account.deposit(20)
my_account.deposit(10)
my_account.withdraw(5)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(5)
my_account.withdraw(15)
my_account.deposit(10)
my_account.withdraw(5)
print(my_account.get_balance(), my_account.get_fees())

# test from another quiz question with two accounts
account1 = BankAccount(10)
account1.withdraw(15)
account2 = BankAccount(15)
account2.deposit(10)
account1.deposit(20)
account2.withdraw(20)
print(account1.get_balance(), account1.get_fees(), account2.get_balance(), account2.get_fees())


# actual from another quiz question
account1 = BankAccount(20)
account1.deposit(10)
account2 = BankAccount(10)
account2.deposit(10)
account2.withdraw(50)
account1.withdraw(15)
account1.withdraw(10)
account2.deposit(30)
account2.withdraw(15)
account1.deposit(5)
account1.withdraw(10)
account2.withdraw(10)
account2.deposit(25)
account2.withdraw(15)
account1.deposit(10)
account1.withdraw(50)
account2.deposit(25)
account2.deposit(25)
account1.deposit(30)
account2.deposit(10)
account1.withdraw(15)
account2.withdraw(10)
account1.withdraw(10)
account2.deposit(15)
account2.deposit(10)
account2.withdraw(15)
account1.deposit(15)
account1.withdraw(20)
account2.withdraw(10)
account2.deposit(5)
account2.withdraw(10)
account1.deposit(10)
account1.deposit(20)
account2.withdraw(10)
account2.deposit(5)
account1.withdraw(15)
account1.withdraw(20)
account1.deposit(5)
account2.deposit(10)
account2.deposit(15)
account2.deposit(20)
account1.withdraw(15)
account2.deposit(10)
account1.deposit(25)
account1.deposit(15)
account1.deposit(10)
account1.withdraw(10)
account1.deposit(10)
account2.deposit(20)
account2.withdraw(15)
account1.withdraw(20)
account1.deposit(5)
account1.deposit(10)
account2.withdraw(20)
print(account1.get_balance(), account1.get_fees(), account2.get_balance(), account2.get_fees())

Question 8#

We will again use the BankAccount class from the previous problem. You should be able to use the same definition for both problems.

Of course, a bank with only one account will go out of business, so we want our BankAccount class to work correctly with many accounts. Naturally, each bank account should have its own balance, with deposits and withdrawals going to the appropriate account. Similarly, the penalty fees for each account should be kept separate.

class BankAccount:
    def __init__(self, initial_balance):
        """Creates an account with the given balance."""
        #…

    def deposit(self, amount):
        """Deposits the amount into the account."""
        #…

    def withdraw(self, amount):
        """
        Withdraws the amount from the account.  Each withdrawal
        resulting in a negative balance also deducts a penalty 
        fee of 5 dollars from the balance.
        """
        #…

    def get_balance(self):
        """Returns the current balance in the account."""
        #…

    def get_fees(self):
        """Returns the total fees ever deducted from the account."""
        #…

Here’s one possible test with multiple accounts. It should print the values 10, 5, 5, and 0.

account1 = BankAccount(10)
account1.withdraw(15)
account2 = BankAccount(15)
account2.deposit(10)
account1.deposit(20)
account2.withdraw(20)
print account1.get_balance(), account1.get_fees(), account2.get_balance(), account2.get_fees()

Copy-and-paste the following much longer test. What four numbers are printed at the end? Enter the four numbers, separated only by spaces.

account1 = BankAccount(20)
account1.deposit(10)
account2 = BankAccount(10)
account2.deposit(10)
account2.withdraw(50)
account1.withdraw(15)
account1.withdraw(10)
account2.deposit(30)
account2.withdraw(15)
account1.deposit(5)
account1.withdraw(10)
account2.withdraw(10)
account2.deposit(25)
account2.withdraw(15)
account1.deposit(10)
account1.withdraw(50)
account2.deposit(25)
account2.deposit(25)
account1.deposit(30)
account2.deposit(10)
account1.withdraw(15)
account2.withdraw(10)
account1.withdraw(10)
account2.deposit(15)
account2.deposit(10)
account2.withdraw(15)
account1.deposit(15)
account1.withdraw(20)
account2.withdraw(10)
account2.deposit(5)
account2.withdraw(10)
account1.deposit(10)
account1.deposit(20)
account2.withdraw(10)
account2.deposit(5)
account1.withdraw(15)
account1.withdraw(20)
account1.deposit(5)
account2.deposit(10)
account2.deposit(15)
account2.deposit(20)
account1.withdraw(15)
account2.deposit(10)
account1.deposit(25)
account1.deposit(15)
account1.deposit(10)
account1.withdraw(10)
account1.deposit(10)
account2.deposit(20)
account2.withdraw(15)
account1.withdraw(20)
account1.deposit(5)
account1.deposit(10)
account2.withdraw(20)
print account1.get_balance(), account1.get_fees(), account2.get_balance(), account2.get_fees()