COSC 235: Programming and Problem Solving

Ch. 4 or… Everything is an ObjectInstructor: Dr. X

Goals

• Understand about objects as computational entities

• Understand and use methods and instance variables

• Use the dot notation• Use the graphics library

Everything is an Object

https://necessaryagitation.files.wordpress.com/2010/04/objects.gif

Everything is an Object

• Objects know stuff• Objects can do stuff• They are not exactly the same as the objects

that surround us• They are… computational entities!• Object Oriented (OO) Programming

Let’s code some objects

• Graphics: create some basic objects and get familiar with the graphics.py library

• We will use the “type” function to figure out what is going on

What did we learn?

• What did the type function reveal?• Where did we see a class before?• What is the difference between a method and

a function?• What is the difference between an instance

variable and a variable?

Everything is an Object

• Objects know stuff – instance variables• Objects can do stuff - methods

Class

• Determines the methods an object will have• An object is an instance of a class

Class vs Object

http://www.dgp.toronto.edu/~meng/courses/108/teaching99/lecture/3week/instance_variable.jpg

Instance Variable

http://www.dgp.toronto.edu/~meng/courses/108/teaching99/lecture/3week/instance_variable.jpg

Method

getName() getName()setName()setName()

Constructor

• A “special” method<class-name>(<param1>, <param2>, …)

• It builds objects

http://www.mymoneysocks.com/wp-content/uploads/2015/01/under_construction.jpeg

Let’s create some clones

Aliasing vs Cloning

• Alias: two variables refer to the same object• Clone: method that makes a copy of an object

Graphing Populations

• We will create a similar program as in the book but for populations

• NEED TO WORK ON EXAMPLE!!!

Event driven programming

• Event ~ Trigger• Event: Object that encapsulates data about

what just happened• Can you thing of example apps that are event

driven?

Event driven program

• Modify the convert.py to convert_gui.py• Add the option to convert meters to feet!