1. Python Programming in Context
Chapter 10

2. Objectives To explore classes and objects further
To understand how to construct a class
To write constructors, accessor methods, and mutator methods
To understand the concept of self
To explore instance data
To implement a graphical simulation using objects

3. Object Oriented Programming
Objects are instances of Classes
Objects can perform methods
Instance Data
What an object knows about itself
Methods
What an object can do

4. Turtle objects Instance Data Methods Color Heading Tail position
Forward
Backward Up

5. Astronomy Design classes to represent planets, sun, moons, etc.
Use these classes to write programs that manipulate the solar system

6. Planet Class
Instance Data
Name
Mass
Distance from sun
radius

7. Listing 10.1
class Planet: def __init__(self, iname, irad, im, idist): self.name = iname self.radius = irad self.mass = im self.distance = idist

8. Figure 10.1

9. Types of Methods Constructor Accessor Mutator
Used to make a new instance of the class
Accessor
Used to get information from an object
Get instance data
Mutator
Used to change something about an object
Change instance data

10. Listing 10.2
def getName(self): return self.name def getRadius(self): return self.radius def getMass(self): return self.mass def getDistance(self): return self.distance

11. Listing 10.3
def getVolume(self): v = 4.0/3 * math.pi * self.radius**3 return v def getSurfaceArea(self): sa = 4.0 * math.pi * self.radius**2 return sa def getDensity(self): d = self.mass / self.getVolume() return d

12. Listing 10.4
def setName(self, newname): self.name = newname

13. Listing 10.5
def show(self): print(self.name)

14. Listing 10.6
def __str__(self): return self.name

15. Figure 10.2

16. Namespaces Namespaces and reference work as they did before
self is the name of the implicit parameter that always refers to the object itself
Never explicitly pass a value to the implicit parameter

17. Figure 10.3

18. Figure 10.4

19. The Sun Class
Instance Data
Name
Mass
Radius
Temperature

20. Listing 10.7
import math class Sun: def __init__(self, iname, irad, im, itemp): self.name = iname self.radius = irad self.mass = im self.temp = itemp def getMass(self): return self.mass def __str__(self): return self.name

21. Solar System Class A sun Many planets
Use a list to keep the collection of planets

22. Listing 10.8
class SolarSystem: def __init__(self, asun): self.thesun = asun self.planets = [] def addPlanet(self, aplanet): self.planets.append(aplanet) def showPlanets(self): for aplanet in self.planets: print(aplanet)

23. Figure 10.5

24. Visualize and Animate Use a turtle to draw the sun and the planets
Animate the solar system by moving the turtle
Need to develop a simple understanding of planetary movement
Velocity
Acceleration
Mass

25. Listing 10.9
class SolarSystem: def __init__(self, width, height): self.thesun = None self.planets = [] self.ssturtle = turtle.Turtle() self.ssturtle.hideturtle() self.ssscreen = turtle.Screen() self.ssscreen.setworldcoordinates(-width/2.0,-height/2.0,width/2.0,height/2.0) def addPlanet(self, aplanet): self.planets.append(aplanet) def addSun(self, asun): self.thesun = asun def showPlanets(self): for aplanet in self.planets: print(aplanet) def freeze(self): self.ssscreen.exitonclick()

26. Listing 10.10
class Sun: def __init__(self, iname, irad, im, itemp): self.name = iname self.radius = irad self.mass = im self.temp = itemp self.x = 0 self.y = 0 self.sturtle = turtle.Turtle() self.sturtle.shape("circle") self.sturtle.color("yellow") #other methods as before def getXPos(self): return self.x def getYPos(self): return self.y

27. Listing 10.11
class Planet: def __init__(self, iname, irad, im, idist, ic): self.name = iname self.radius = irad self.mass = im self.distance = idist self.x = idist self.y = 0 self.color = ic self.pturtle = turtle.Turtle() self.pturtle.color(self.color) self.pturtle.shape("circle") self.pturtle.up() self.pturtle.goto(self.x,self.y) self.pturtle.down() #other methods as before def getXPos(self): return self.x def getYPos(self): return self.y

28. Figure 10.6

29. Figure 10.7

30. Figure 10.8

31. Listing 10.12
class Planet: def __init__(self, iname, irad, im, idist, ivx, ivy, ic): #other instance variables as before self.velx = ivx self.vely = ivy

32. Listing 10.13
def moveTo(self, newx, newy): self.x = newx self.y = newy self.pturtle.goto(newx, newy) def getXVel(self): return self.velx def getYVel(self): return self.vely def setXVel(self, newvx): self.velx = newvx def setYVel(self, newvy): self.vely = newvy

33. Listing 10.14
def movePlanets(self): G = .1 dt = .001 for p in self.planets: p.moveTo(p.getXPos() + dt * p.getXVel(), p.getYPos() + dt * p.getYVel()) rx = self.thesun.getXPos() - p.getXPos() ry = self.thesun.getYPos() - p.getYPos() r = math.sqrt(rx**2 + ry**2) accx = G * self.thesun.getMass()*rx/r**3 accy = G * self.thesun.getMass()*ry/r**3 p.setXVel(p.getXVel() + dt * accx) p.setYVel(p.getYVel() + dt * accy)

34. Listing 10.15
def createSSandAnimate(): ss = SolarSystem(2,2) sun = Sun("SUN", 5000, 10, 5800) ss.addSun(sun) m = Planet("MERCURY", 19.5, 1000, .25, 0, 2, "blue") ss.addPlanet(m) m = Planet("EARTH", 47.5, 5000, 0.3, 0, 2.0, "green") m = Planet("MARS", 50, 9000, 0.5, 0, 1.63, "red") m = Planet("JUPITER", 100, 49000, 0.7, 0, 1, "black") numTimePeriods = 2000 for amove in range(numTimePeriods): ss.movePlanets() ss.freeze() createSSandAnimate()

35. Figure 10.9