Python Programming in Context Chapter 10

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

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

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

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

Planet Class Instance Data Name Mass Distance from sun radius

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

Figure 10.1

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

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

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

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

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

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

Figure 10.2

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

Figure 10.3

Figure 10.4

The Sun Class Instance Data Name Mass Radius Temperature

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

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

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)

Figure 10.5

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

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()

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

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

Figure 10.6

Figure 10.7

Figure 10.8

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

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

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)

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()

Figure 10.9