Transcript PythonContextCH10x

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
– Color
– Heading
– Tail position
• Methods
– 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
– 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")
ss.addPlanet(m)
m = Planet("MARS", 50, 9000, 0.5, 0, 1.63, "red")
ss.addPlanet(m)
m = Planet("JUPITER", 100, 49000, 0.7, 0, 1, "black")
ss.addPlanet(m)
numTimePeriods = 2000
for amove in range(numTimePeriods):
ss.movePlanets()
ss.freeze()
createSSandAnimate()
Figure 10.9