INFO 206 Lab Exercise 1 Introduction to Classes and Objects 1/18/2012i206 Lab 1 - Exercise1

Reference Object “An object associates data with the particular operations that can use or affect that data.” ~ Apple “Similar to the real-world, objects have both state and behavior.” ~Java Objects encapsulate both data and methods that interacts with the data. Objects can store data in fields, also known as instance variables (attributes) – Attributes can be a variety of data types – Attributes can also store references to other objects Objects can have methods An object’s attributes and methods are defined by its class 1/18/2012i206 Lab 1 - Exercise2

Reference Class: The class is the blueprint for creating an object. The class definition declares the data fields that become part of every object of the class, and it defines a set of methods that all objects in the class can use. Classes are used to create objects, which are then called “instances” of that class A method is a function that is associated with a particular class. Unlike a function, a method has to be called by an instance of the class where the method was defined. 1/18/2012i206 Lab 1 - Exercise3

Lab Exercise The Bank Account Class The object-oriented bank account example is a common demonstration of OOP by modeling a bank account class. Let’s see if we can do the same. We’ll create a program called PythonBanking. Let’s start by launching your favorite IDE for Python programming. 1/18/2012i206 Lab 1 - Exercise4

Lab Exercise - Style Guidelines 1.The first line of all your python programs must be: #!/usr/bin/env python – “#!” a.k.a. shebang indicates that the file is a script – “/usr/bin/env python” tells the computer to use this interpreter to read this file 2.Set your full name in the __author__ special attribute at the top of each python file 3.Set your in the __ __ special 4.Set your python version in the __python_version attribute – You can determine your python version by typing this in the command line: >>python –version 5.__can_anonymously_use_as_example specifies whether or not we can use your code (or portion of your code) anonymously for example and/or demonstration 1/18/2012i206 Lab 1 - Exercise5

Lab Exercise - Style Guidelines Example header of a python program: #!/usr/bin/env python __author__ = 'Alex Chung' __ __ = __python_version = '2.6.1' __can_anonymously_use_as_example = True 1/18/2012i206 Lab 1 - Exercise6

Lab Exercise - Declaring a Python Class Before an object can be instantiated we first need to define the “blueprint” for the object with class definition: class BankAccount(object): “””represents a generic banking account””” This header indicates that the new class is a BankAccount, which inherits from the generic object class. The body is where we define the class variables and functions but currently it is empty. To create a BankAccount object, you call BankAccount like a function: personalAccount = BankAccount() The return value is a reference to a BankAccount object. Creating a new object is called instantiation, and the object is an instance of the class. 1/18/2012i206 Lab 1 - Exercise7

Let’s extend our BankAccount class to add class attributes to hold the account name and number. class BankAccount(object): “””represents a generic banking account””” name = “” accountNumber = “” balance = 0 We can assign values to the attributes with dot notation: personalAccount.name = “Alex Chung” personalAccount.accountNumber = “234324ff3” personalAccount.balance = We can also use the dot notation to access the values of the object’s attributes: >>>print(personalAccount.name) Alex Chung >>>print(personalAccount.accountNumber) ff3 Lab Exercise – Defining Class Attributes 1/18/2012i206 Lab 1 - Exercise8

We can also use the init (short for initialization) method that gets invoked when an object is instantiated: #inside class BankAccount def __init__(self, accountName, accountNumber, accountBalance): self.name = accountName self.accountNumber = accountNumber self.balance = accountBalance To create a BankAccount object with __init__: personalAccount = BankAccount(“Alex Chung”, “234324ff3”, ) Lab Exercise – Defining Class Attributes 1/18/2012i206 Lab 1 - Exercise9

Methods are semantically the same as functions, in which, they can take arguments and return a result. However, methods are defined inside a class definition and they are called explicitly by the class’ instances. For example, we want to deposit money into a bank account. # inside class BankAccount: def deposit(self, amount): self.balance = self.balance + amount Using the earlier personalAccount: >>>personalAccount = BankAccount(“Alex Chung”, “234324ff3”, ) >>>personalAccount.deposit(100.0) >>>print(personalAccount.balance) Lab Exercise – Adding Methods to Class 1/18/2012i206 Lab 1 - Exercise10

Lab Exercise Your code should look like this: #!/usr/bin/env python __author__ = 'Alex Chung' __ __ = __python_version = '3.2.2' __can_anonymously_use_as_example = 'True' """OOP Demonstration with Bank Account Program""" class BankAccount(object): """represents a generic banking account""" def __init__(self, accountName, accountNumber, accountBalance): self.name = accountName self.accountNumber = accountNumber self.balance = accountBalance def deposit(self, amount): self.balance = self.balance + amount personalAccount = BankAccount("Alex Chung", "233444", ) print (personalAccount.balance) personalAccount.deposit(100.0) print (personalAccount.balance) 1/18/2012i206 Lab 1 - Exercise11

A Little Extra Modify the BankAccount class to help John Doe figure out his ending balance. John Doe opens a new savings account with $50. He earns monthly (every 30 days) 5% interest if his account has a balance of < $500 and 10% if his balance exceeds $500. What will his ending balance be after 6 months if he deposits $200 every 30 days (after his initial deposit of $50 at day 0). 1/18/2012i206 Lab 1 - Exercise12