Homework 11

Due at 11:59:59 pm on Saturday, 11/30/2019.

Instructions

Download hw11.zip. Inside the archive, you will find starter files for the questions in this homework, along with a copy of the OK autograder.

Submission: When you are done, submit with python3 ok --submit. You may submit more than once before the deadline; only the final submission will be scored. Check that you have successfully submitted your code on okpy.org. See this article for more instructions on okpy and submitting assignments.

Readings: This homework relies on following references:

Question 1: Account

There are several things wrong with the following code! Debug the Account class to satisfy the docstring.

class Account(object):
    """A bank account that allows deposits and withdrawals.

    >>> sophia_account = Account('Sophia')
    >>> sophia_account.deposit(1000000)   # depositing my paycheck for the week
    1000000
    >>> sophia_account.transactions
    [('deposit', 1000000)]
    >>> sophia_account.withdraw(100)      # buying dinner
    999900
    >>> sophia_account.transactions
    [('deposit', 1000000), ('withdraw', 100)]
    """

    interest = 0.02
    balance = 1000

    def __init__(self, account_holder):
        self.balance = 0
        self.holder = account_holder
        self.transactions = []

    def deposit(self, amount):
        """Increase the account balance by amount and return the
        new balance.
        """
        self.transactions.append(('deposit', amount))
        Account.balance = self.balance + amount
        return self.balance

    def withdraw(self, amount):
        """Decrease the account balance by amount and return the
        new balance.
        """
        self.transactions.append(('withdraw', amount))
        if amount > self.balance:
            return 'Insufficient funds'
        self.balance = Account.balance - amount
        return Account.balance

Use OK to test your code:

python3 ok -q Account

Question 2: Checking account

We'd like to be able to cash checks, so let's add a deposit_check method to our CheckingAccount class. It will take a Check object as an argument, and check to see if the payable_to attribute matches the CheckingAccount's holder. If so, it marks the Check as deposited, and adds the amount specified to the CheckingAccount's total.

Write an appropriate Check class, and add the deposit_check method to the CheckingAccount class. Make sure not to copy and paste code! Use inheritance whenever possible.

See the doctests for examples of how this code should work.

class CheckingAccount(Account):
    """A bank account that charges for withdrawals.

    >>> check = Check("Steven", 42)  # 42 dollars, payable to Steven
    >>> steven_account = CheckingAccount("Steven")
    >>> eric_account = CheckingAccount("Eric")
    >>> eric_account.deposit_check(check)  # trying to steal steven's money
    The police have been notified.
    >>> eric_account.balance
    0
    >>> check.deposited
    False
    >>> steven_account.balance
    0
    >>> steven_account.deposit_check(check)
    42
    >>> check.deposited
    True
    >>> steven_account.deposit_check(check)  # can't cash check twice
    The police have been notified.
    """
    withdraw_fee = 1
    interest = 0.01

    def withdraw(self, amount):
        return Account.withdraw(self, amount + self.withdraw_fee)



class Check(object):
    "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q CheckingAccount

Question 3: Errors

It is often said that nothing in life is certain but death and taxes. For a programmer or data scientist, however, nothing is certain but encountering errors.

In Python, there are two primary types of errors, both of which you are likely familiar with: syntax errors and exceptions. Syntax errors occur when the proper structure of the language is not followed, while exceptions are errors that occur during the execution of a program. These include errors such as ZeroDivisionError, TypeError, NameError, and many more!

Under the hood, these errors are based in the concepts of object orientation, and all exceptions are class objects. If you're interested in more detailed explanations of the structure of exceptions as well as how to create your own, check out this article from the Python documentation! In the meantime, we'll implement our own version of an Error class

Complete the Error, SyntaxError, and ZeroDivisionError classes such that they create the correct messages when called.

  • The SyntaxError and ZeroDivisionError classes inherit from the Error class and add functionality that is unique to those particular errors. Their code is partially implemented for you.
  • The add_code method adds a new helpful message to your error, while the write method should print the output that you see when an error is raised.
  • You can access the parent class methods using the super() function
class Error:
    """
    >>> err1 = Error(12, "error.py")
    >>> err1.write()
    'error.py:12'

    """
    def __init__(self, line, file):
        "*** YOUR CODE HERE ***"

    def write(self):
        return self.file + ':' + str(self.line)

class SyntaxError(Error):
    """
    >>> err1 = SyntaxError(17, "HW10.py")
    >>> err1.write()
    HW10.py:17 SyntaxError : Invalid syntax
    >>> err1.add_code(4, "EOL while scanning string literal")
    >>> err2 = SyntaxError(18, "HW10.py", 4)
    >>> err2.write()
    HW10.py:18 SyntaxError : EOL while scanning string literal

    """
    type = 'SyntaxError'
    msgs = {0 : "Invalid syntax", 1: "Unmatched parentheses", 2: "Incorrect indentation", 3: "missing colon"}

    def __init__(self, line, file, code=0):
        "*** YOUR CODE HERE ***"

    def write(self):
        end = self.type + ' : ' + self.message
        "*** YOUR CODE HERE ***"

    def add_code(self, code, msg):
        "*** YOUR CODE HERE ***"

class ZeroDivisionError(Error):
    """
    >>> err1 = ZeroDivisionError(273, "HW10.py")
    >>> err1.write()
    HW10.py:273 ZeroDivisionError : division by zero
    """
    type = 'ZeroDivisionError'

    def __init__(self, line, file, message='division by zero'):
        "*** YOUR CODE HERE ***"

    def write(self):
        end = self.type + ' : ' + self.message
        "*** YOUR CODE HERE ***"

Use OK to test your code:

python3 ok -q Error

Use OK to test your code:

python3 ok -q SyntaxError

Use OK to test your code:

python3 ok -q ZeroDivisionError

Question 4: Project

Nothing to submit for this question, just a reminder to work on your project! Good luck!