Introduction to Object-Oriented Programming Concepts

INFO 206 Lab Exercise 1 Introduction to Classes and Objects 1/23/2013 i206 Lab 1 - Exercise 1

Logistics What development environments are people using? 1/23/2013 i206 Lab 1 - Exercise 2

Logistics Python version: let s decide as a class. 1/23/2013 i206 Lab 1 - Exercise 3

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 1/23/2013 i206 Lab 1 - Exercise 4

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. 1/23/2013 i206 Lab 1 - Exercise 5

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. 1/23/2013 i206 Lab 1 - Exercise 6

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 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: 2. 3. 4. >>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 1/23/2013 i206 Lab 1 - Exercise 7

Lab Exercise - Style Guidelines Example header of a python program: #!/usr/bin/env python __author__ = Sarah Van Wart' __email__ = vanwars@ischool.berkeley.edu' __python_version = 3.2.3' __can_anonymously_use_as_example = True 1/23/2013 i206 Lab 1 - Exercise 8

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. 1/23/2013 i206 Lab 1 - Exercise 9

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 = Sarah Van Wart personalAccount.accountNumber = 6498-0001 personalAccount.balance = 100.0 We can also use the dot notation to access the values of the object s attributes: >>>print(personalAccount.name) Sarah Van Wart >>>print(personalAccount.accountNumber) 6498-0001 1/23/2013 i206 Lab 1 - Exercise 10

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( SarahVan Wart , 6498-0001 , 1000.0) 1/23/2013 i206 Lab 1 - Exercise 11

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 1/23/2013 i206 Lab 1 - Exercise 12

Lab Exercise Your code should look like this: #!/usr/bin/env python __author__ = Sarah Van Wart' __email__ = vanwars@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 if __name__=="__main__": pa = BankAccount('Sarah Van Wart', '6498-0001', 0.0) pa.deposit(10) print(pa.name, pa.balance) 1/23/2013 i206 Lab 1 - Exercise 13

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)? 1/23/2013 i206 Lab 1 - Exercise 14