INFO 206 Lab Exercise 1

1. INFO 206 Lab Exercise 1 Introduction to Classes and Objects i206 Lab 1 - Exercise

2. 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 i206 Lab 1 - Exercise

3. 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. i206 Lab 1 - Exercise

4. 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. i206 Lab 1 - Exercise

5. Lab Exercise - Style Guidelines • 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 • Set your full name in the __author__ special attribute at the top of each python file • Set your name@ischool.edu email in the __email__ special attribute • Set your python version in the __python_version attribute • You can determine your python version by typing this in the command line: >>python –version • __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 i206 Lab 1 - Exercise

6. Lab Exercise - Style Guidelines Example header of a python program: #!/usr/bin/env python __author__ = 'Alex Chung' __email__ = 'achung@ischool.berkeley.edu' __python_version = '2.6.1' __can_anonymously_use_as_example = True i206 Lab 1 - Exercise

7. 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. i206 Lab 1 - Exercise

8. Lab Exercise – Defining Class Attributes 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 = 100.0 We can also use the dot notation to access the values of the object’s attributes: >>>print(personalAccount.name) Alex Chung >>>print(personalAccount.accountNumber) 234324ff3 i206 Lab 1 - Exercise

9. Lab Exercise – Defining Class Attributes 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”, 1000.0) i206 Lab 1 - Exercise

10. Lab Exercise – Adding Methods to Class 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”, 1000.0) >>>personalAccount.deposit(100.0) >>>print(personalAccount.balance) 1100.0 i206 Lab 1 - Exercise

11. Lab Exercise Your code should look like this: #!/usr/bin/env python __author__ = 'Alex Chung' __email__ = 'achung@ischool.berkeley.edu' __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", 1000.0) print (personalAccount.balance) personalAccount.deposit(100.0) print (personalAccount.balance) i206 Lab 1 - Exercise

12. 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). i206 Lab 1 - Exercise