[Tutor] Trouble with exercise regarding classes
amartin7211 at gmail.com
Wed Aug 25 23:48:11 CEST 2010
I just starting programming and am trying to learn some python (ver 2.6). I
am reading Python Programming: An Introduction to Computer Science by John
Zelle. In chapter ten, the first programming exercise asks the reader to
modify code from the chapter (below) . The code I added is highlighted.
However, when I did so I got this error: "TypeError: unbound method getY()
must be called with Projectile instance as first argument (got nothing
instead) " Can someone help me out with what I am doing wrong? Please be as
straitforward as you can. I am still struggling with classes
Thanks a lot
> # Simulation of the flight of a cannon ball (or other projectile)
> # This version uses a separate projectile module file
> from projectile import Projectile
> def getInputs():
> a = input("Enter the launch angle (in degrees): ")
> v = input("Enter the initial velocity (in meters/sec): ")
> h = input("Enter the initial height (in meters): ")
> t = input("Enter the time interval between position calculations: ")
> return a,v,h,t
> def main():
> angle, vel, h0, time = getInputs()
> cball = Projectile(angle, vel, h0)
> zenith = 0.0
> while cball.getY() >= 0:
> if Projectile.getY > zenith:
> zenith = Projectile.getY()
> print "\nDistance traveled: %0.1f meters." % (cball.getX())
> print "The heighest the cannon ball reached was %0.1f meters." %
> if __name__ == "__main__": main()
> Provides a simple class for modeling the flight of projectiles."""
> from math import pi, sin, cos
> class Projectile:
> """Simulates the flight of simple projectiles near the earth's
> surface, ignoring wind resistance. Tracking is done in two
> dimensions, height (y) and distance (x)."""
> def __init__(self, angle, velocity, height):
> """Create a projectile with given launch angle, initial
> velocity and height."""
> self.xpos = 0.0
> self.ypos = height
> theta = pi * angle / 180.0
> self.xvel = velocity * cos(theta)
> self.yvel = velocity * sin(theta)
> def update(self, time):
> """Update the state of this projectile to move it time seconds
> farther into its flight"""
> self.xpos = self.xpos + time * self.xvel
> yvel1 = self.yvel - 9.8 * time
> self.ypos = self.ypos + time * (self.yvel + yvel1) / 2.0
> self.yvel = yvel1
> def getY(self):
> "Returns the y position (height) of this projectile."
> return self.ypos
> def getX(self):
> "Returns the x position (distance) of this projectile."
> return self.xpos
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