[Visualpython-users] Repeating VPython simulation multiple times

Hi, I found out why I didn't see the VPython simulation window except the
first time.
I set scene.exit to 0 because I wanted to close only the VPython simulation
window rather than the whole application. I expected "scene.exit = 0" to a
"REAL" clsoing, but apparently it is not. It seems like it just set
scene.visible to "0".
When I manually set "scene.visible" to "1" for later simulation, the VPython
simulation window appeared. But VPython objects created in the previous
simulation were still there.
I tried to set all the spheres created in the previous simulation by setting
them to None, it didn't work.
Is there any way to clear all the objects in the scene when it is closed?
Thanks.

YJ

# Button ID
BT_START = 10

from wxPython.wx import *
from wxPython.html import wxHtmlWindow
from visual import *

class CPFreeFall1D_InitialPane( wxHtmlWindow ):
    def __init__( self, parent, id, **kwargs ):
        wxHtmlWindow.__init__( self, parent, id, **kwargs )
        wxButton( self, BT_START, "Start Simulation", wxPoint( 100, 100 ) )
        EVT_BUTTON( self, BT_START, self.OnClickStart )

    def OnClickStart( self, event ):
        # read the configuration file
        import ConfigParser
        cfg = ConfigParser.ConfigParser()
        cfg.read( 'freefall1d.cfg' )

        self.startSimulation( cfg )

    def startSimulation( self, cfg ):
        print 'start simulation'

        scene.width = scene.height = 500.
        scene.x = scene.y = 0
        scene.forward = ( -0.2, -0.5, -1 )
        scene.autoscale = 0
        scene.userzoom = 0
        scene.range = ( 15, 15, 15 )
        scene.exit = 0  # only close the simulation window

        # clean up the previous simulation result, but it didn't work.
        for obj in scene.objects:
            if obj.__class__ == 'sphere':
                print obj
                obj = None

        # start an actual simulation
        scene.select()
        xmax = 10
        dx = xmax / 5
        grid = []
        gravity = cfg.get( 'Characteristics', 'gravity' )
        r = float( cfg.get( 'Characteristics', 'diameter' ) ) / 2

        # make the scene visible
        # it should be done automatically, but it is not the case.
        # So I call it by myself.
        scene.visible = 1

        for x in arange( -xmax, xmax+dx, dx ):
            grid.append( curve( pos = [(x, 0, -xmax), (x, 0, xmax)],
                                color = ( .7, .7, .7 ) ) )

        for z in arange( -xmax, xmax+dx, dx ):
            grid.append( curve( pos = [(-xmax, 0, z), (xmax, 0, z)],
                                color = (.7, .7, .7) ) )


        ball = sphere(pos=(0,8,0), radius=r, color=color.red)
        ball.selected = 0
        ball.velocity = vector(0,-1,0)
        dt = 0.1

        ballPosition = []
        ballVelocity = []
        t = []
        currentT = 0

        while ball.y > ball.radius:
            rate(10)
            ball.pos = ball.pos + ball.velocity*dt
            ball.velocity.y = ball.velocity.y - float(gravity)*dt
            wake = sphere( pos = ball.pos, radius = 0.1, color =
color.blue )
            t.append( currentT + dt )
            ballPosition.append( ball.pos.y )
            ballVelocity.append( ball.velocity.y )
            currentT = currentT + dt

        print 'end simulation'