VPython Quick Reference

Arithmetic + - * / ** (exponentiate) % (modulus)

Shortcuts += -= *= /=

Comparisons == != < <= > >=

Logic and or not True False

Math functions cos(t) acos(x) log(x)(natural log)sin(t) asin(x) exp(x)(e^x)tan(t) atan(x) atan2(y,x) (angle in polar coordinates)abs(x) sqrt(x) pow(x,y)(x^y)round(x) floor(x) ceil(x) int(x) (round normally, down, up, or toward zero)max(x,y,...) min(x,y,...) factorial(n) combin(m,n) pi(3.14...) random() (pseudo-random number between 0 and 1)

Control structures

if balance >= 1000:
    print("You're rich!")
elif balance > 0:
    print("Keep saving pennies!")
else:
    print("You're broke.")

while t < 10:
    t += dt
    doStuff()

for i in range(100):
    print("I love VPython!")

Function definitions

def startStop():
    global running
    running = not running

def hypotenuse(a, b):
    return sqrt(a*a + b*b)

Formatting numbers

"{:.3f}".format(theNumber)    # round to 3 decimal places

Lists (arrays)

x = []                        # create an empty list
for i in range(100):
    x.append(initialValue)    # build the list
x[0] = aValue                 # first entry has index 0
x[99] = x[98] + dx            # last entry is 99; x[100] doesn't exist

3D shapes

box(pos=vec1, size=vec2, color=vec3)
sphere(pos=vec1, radius=num1, color=vec2)
cylinder(pos=vec1, axis=vec2, radius=num1, color=vec3)
spaceVector = vector(x,y,z)
colorVector = vector(r,g,b)   # values between 0 and 1

Scene attributes

scene.width = w               # in nominal screen pixels
scene.height = h
scene.resizable = False       # turns off user resizing
scene.background = aColor
scene.center = vector(x,y,z)
scene.range = r               # from center to edge
scene.fov = theta             # field of view in radians (make tiny for 2D look)
scene.autoscale = False       # turns off auto-scaling
scene.userzoom = False        # turns off zoomability
scene.userspin = False        # turns off rotatability

Animation

while y > 0:
    rate(60)                  # try to run at 60 iterations per second
    ball.pos = vector(newx, newy, newz)

Leaving a trail

ball = sphere(make_trail=True, trail_type="points", interval=10)
ball.clear_trail()

Plotting a graph

graph(title="A Graph", xtitle="t (s)", ytitle="x (m)", width=450, height=300,
        align="right", background=color.white)
xDots = gdots(color=color.green, size=1, interval=10)
xDots.plot(t,x)               # add a point to the graph
xDots.delete()                # delete all dots and start over

GUI widgets

button(text="Start/stop", bind=startStop)
xSlider = slider(left=10, length=200, min=0, max=5, step=1, value=2, bind=adjustx)
readout = wtext(text="25")
scene.append_to_caption("\n\n")   # \n is new line

http://physics.weber.edu/schroeder/scicomp/