Introduction to Object-Oriented Programming in Python

1. Introduction to Object-Oriented Programming in Python Barb Ericson Georgia Institute of Technology July 2009 06-Intro-Object-Oriented-Prog

2. Learning Goals • Compare procedural programming and object-oriented programming • Introduce computation as simulation • Create objects in Python • Invoke methods on objects in Python • Create a subclass • Create a method in a class • Pass a parameter to a method in a class 06-Intro-Object-Oriented-Prog

3. Procedural Programming • Focus is on the procedures • The tasks that need to be done • Break large tasks into smaller tasks • Write a function for each task • Problems with procedural • The data is passed around and any function can change the data • It is hard to find the function • They can be in many files with many names 06-Intro-Object-Oriented-Prog

4. Object-Oriented Programming • The focus is on who does each task as well as the tasks to be done • Responsibility driven • Advantages • Manage complexity by distributing responsibility across objects • Make systems robust by making objects work independently • Support reuse because objects provide services 06-Intro-Object-Oriented-Prog

5. Computers as Simulators • “The computer is the Proteus of machines. Its essence is its universality, its power to simulate. Because it can take on a thousand forms and serve a thousand functions, it can appeal to a thousand tastes.” Seymour Papert in Mindstorms 06-Intro-Object-Oriented-Prog

6. Creating a Simulation • Computers let us simulate things • We do this by creating models of the things we want to simulate • We need to define what types of objects we will want in our simulation and what they can do • Classes define the types and create objects of that type • Objects act in the simulation 06-Intro-Object-Oriented-Prog

7. Creating objects • We have been creating objects in Python using • makePicture(file) • makeSound(file) • But, these are functions we created to make it easy to create objects from these classes 06-Intro-Object-Oriented-Prog

8. Creating objects in python • Use ClassName(value1,value2,…) • Picture(file) # create a picture • Sound(file) # create a sound • World() # create a world • Name the objects that are created >>> earth = World() >>> tina = Turtle(earth) >>> sue = Turtle(earth) • Use the name to ask the object to do something objName.function() >>> tina.forward() 06-Intro-Object-Oriented-Prog

9. Turtle Behaviors • forward() # forward by 100 pixels • forward(amount) # forward by amount • turnLeft() # 90 degree left • turnRight() # 90 degree right • turn(degrees) # pos right and neg is left • penUp() # pick up the pen • penDown() # put pen down • moveTo(x,y) # move to x and y location • setColor(blue) # set the color • setPenWidth(width) # size of pen trail • setVisible(false) # don't draw turtle 06-Intro-Object-Oriented-Prog

10. Challenge • Use a turtle to draw a square • Use a turtle to draw blocks of color using a wide pen trail 06-Intro-Object-Oriented-Prog

11. Create a Subclass class SmartTurtle(Turtle): def drawSquare(self): for i in range (0 ,4): self.turnRight () self.forward () >>> earth1 = World() >>> smarty = SmartTurtle(earth1) >>> smarty.drawSquare() 06-Intro-Object-Oriented-Prog

12. Passing Parameters to Methods class SmartTurtle(Turtle): def drawSquare(self): for i in range (0 ,4): self.turnRight () self.forward () def drawSquare(self, width): for i in range (0 ,4): self.turnRight () self.forward(width) >>> mars = World () >>> tina = SmartTurtle(mars) >>> tina.drawSquare (30) >>> tina.drawSquare (150) >>> tina.drawSquare (100) 06-Intro-Object-Oriented-Prog

13. Creating the Slide Class class Slide: def show(self): show(self.picture) blockingPlay(self.sound) >>> slide1=Slide() >>> slide1.picture = makePicture(getMediaPath("barbara.jpg")) >>> slide1.sound = makeSound(getMediaPath("bassoon-c4.wav")) >>> slide1.show() 06-Intro-Object-Oriented-Prog

14. Constructors class slide: def __init__(self , pictureFile ,soundFile ): self.picture = makePicture(pictureFile) self.sound = makeSound(soundFile) def show(self ): show(self.picture) blockingPlay(self.sound) 06-Intro-Object-Oriented-Prog

15. Testing the constructor def playSlideShow2 (): pictF = getMediaPath("barbara.jpg") soundF = getMediaPath("bassoon -c4.wav") slide1 = slide(pictF ,soundF) pictF = getMediaPath("beach.jpg") soundF = getMediaPath("bassoon -e4.wav") slide2 = slide(pictF ,soundF) pictF = getMediaPath("church.jpg") soundF = getMediaPath("bassoon -g4.wav") slide3 = slide(pictF ,soundF) pictF = getMediaPath("jungle2.jpg") soundF = getMediaPath("bassoon -c4.wav") slide4 = slide(pictF ,soundF) slide1.show () slide2.show () slide3.show () slide4.show () 06-Intro-Object-Oriented-Prog

16. Object-oriented with Pictures >>> pic=Picture(getMediaPath("barbara.jpg")) >>> pic.show() >>> pic.getWidth() >>> pic.getHeight() >>> pixels = pic.getPixels() >>> pixel = pic.getPixel(0,0) >>> color = pixel.getColor(); >>> red = pixel.getRed() 06-Intro-Object-Oriented-Prog

17. Picture Functions def show(picture ): if not picture.__class__ == Picture: print "show(picture ): Input is not a picture" raise ValueError picture.show () 06-Intro-Object-Oriented-Prog

18. Summary • Procedural programming has a focus on the procedures (tasks) • Object-oriented programming has a focus on the objects and on simulation • You can create objects from classes in Python • Picture(file) or Class(parameters) • You can create subclasses in Python • class SmartTurtle(Turtle): • You can overload methods by passing different parameters 06-Intro-Object-Oriented-Prog