[Visualpython-users] Starting and stopping Vpython programs from Pythonwin

As you probably know, if you just close a Vpython display which was started
from a program running under Pythonwin, it causes Pythonwin to die, even
after the program terminates.

So I had to "invent" a method of gracefully terminating a Vpython program.
Not too difficult I know, but having done so, I thought I might as well
share it. So here is a function (a histogram plotter), with this capability.

#!/usr/bin/python
#
# Histo - plot a histogram of stacked cylinders using Vpython
#
# Author Patrick Keogh
#
from visual import *

def histo(stacked, data):
    """ The second parameter which is passed is assumed to be a sequence,
    which has:
        - The first element is a sequence of category labels
        - The second element is a sequence of data series labels.
        - The third element is a sequence of sequences of the data values
    """
#
# This try/except figures out if there is already a scene. If not, it
creates it.
#
    try:
        type(scene)
    except:
        scene = display()
        scene.show()
    max_entries = len(data[0])
    col = (color.red,color.blue,color.green,color.yellow)
    data_array = []
    for i in data[2]:
        max_entries = max((max_entries, len(i)))
    arrow(axis=(max_entries+1,0,0), shaftwidth=0.1, fixedwidth=1)
    max_height = 0.0
    for i in range(max_entries):
        data_array.append([])
        for j in range(len(data[2])):
            data_array[i].append(data[2][j][i])
        max_height=max((max_height,sum(data_array[i])))
    arrow(axis=(0,10,0), shaftwidth=0.1, fixedwidth=1)
    for j in range(len(data_array[0])):

label(pos=(-5,j*2,j*2),text=data[1][j],color=col[j],opacity=0,box=0,border=0
)
    for i in range(len(data_array)):
        base = 0
        for j in range(len(data_array[i])):
            cyl_height = data_array[i][j]*10.0/max_height
            if stacked:
                pos = (i+1,base,0)
                base = base + cyl_height
            else:
                pos = (i+1,0,j*2)
            axis = (0,cyl_height,0)
            c = cylinder(pos=pos,axis=axis,radius=0.3,color=col[j])
            c.label = "(" + data[0][i] + "," + repr(data_array[i][j]) + ")"
    scene.center = (len(data_array)/2,5,0)
    again = 1
    prev = None
#
# Apart from the standard zoom and rotate capabilities, we will add
#
#	Left click		= Set a new center
#	Ctrl-C		= Exit
#	Move over a bar	= Display the (x,y) label for the histogram bar
#				  Note the "hack" of inserting the label as an attribute of the
cylinder
#
    while again:
        while scene.mouse.events:
            if scene.mouse.clicked:
                scene.center = scene.mouse.getclick().pos
        if scene.kb.keys:
            if scene.kb.getkey() == 'ctrl+c':
               again = 0
        if scene.mouse.pick <> None:
            if prev <> scene.mouse.pick:
                try:
                    l.visible = 0
                except:
                    pass
                prev = scene.mouse.pick
                if prev.__class__ == cylinder:
                    l = label(pos=scene.mouse.pos, text=prev.label, box=0)
#
# If a control-c was entered, then the while loop exits, and we close down
the display and exit
#
    scene.hide()
    del(scene)