CS Assignment 01: Python classes and inheritance Solution

Background: A class serves as the primary means for abstraction in object-oriented programming. In Python, every piece of data is an instance of some class. A class provides a set of behaviors in the form of member functions (also known as methods) with implementations that are common to all instances of that class. A class serves as a blueprint for its instances, determining the way that state information for each instance is represented in the form of attributes (also known as fields, instance variables, or data members). In object-oriented programming, inheritance allows a new class to be defined based upon an existing class as the starting point. The base class is also known as parent or super-class, while the newly defined class is known as the subclass or child.

In this assignment, we will work with classes and inheritance in python, and do some simple testing on our class to ensure correctness of our methods.

Your job is to create three classes:

    1. BankAccount

    2. ChequingAccount

    3. SavingsAccount

BankAccount must be an ‘abstract base class’ (see section 2.4.3 of LECTURE_02_NOTES). ChequingAccount and SavingsAccount must both inherit from BankAccount (see section 2.4.1 of LECTURE_02_NOTES).

BankAccount must be constructed with 3 arguments to __init__ which are:

    1. Name of the person who owns the bank account (string)

    2. Name of the bank (string)

    3. Initial balance (float)

BankAccount must implement the following methods

    1. deposit(amount) – adds amount to balance

    2. withdraw(amount) – attempts to subtract amount from balance.

a.  Returns True if balance – amount > 0, and False otherwise

ChequingAccount, which inherits from BankAccount, must take an additional argument to __init__ which is transaction_fee.

ChequingAccount must also implement the method make_purchase(amount) which will call the withdraw function of the super class, and apply transaction_fee after withdraw returns.

SavingsAccount, which also inherits from BankAccount, must take an additional argument to __init__ which is interest_rate (a float between 0 and 0.025).

SavingsAccount must implement the method accrue_interest which will calculate the interest on balance and increase balance by the amount: interest_rate * balance .

Tests:

In __main__ (see ‘testing the class’ in section 2.3 of LECTURE_02_NOTES) provide method coverage and statement coverage for your ChequingAccount and SavingsAccount classes. Method coverage means your tests should call every method of the class at least once, and statement coverage means your tests should result in the execution of every statement in the class at least once (so method coverage is actually a subset of statement coverage).

Operator overloading:

In table 2.1 of LECTURE_02_NOTES, overloaded operations are shown along with Python’s corresponding special methods. Implement the +=, -=, <, and > operators for your BankAccount class by defining the corresponding method (for example, the corresponding method to ‘+=’ is __iadd__. The operator overloading methods should have the following behavior:

+= and -= should add to or subtract from the bank account’s balance.

    • and > should compare two bank account balances. For example, if a.__lt__(b) is called, it will return True if the balance field of BankAccount a is less than the balance field of BankAccount b.

Be sure to include tests for your overloaded operator methods!

Include 3 source files in your moodle submission:

    1) BankAccount (no tests needed because it is an abstract class

    2) ChequingAccount (include the tests at the bottom)

    3) SavingsAccount (include the tests at the bottom)