Error with a VPython code that works at glowscript.org, but output error in Jupyerlab

I am a newbie in VPython and I try to run very simple code from examples.

The following code works perfectly at glowscript.org :

Web VPython 3.2
coaster = curve(vector(-3,0,0),vector(-3,0,0))
theta = pi
d_theta = pi/100
while (theta <= 3*pi/2):
    theta += d_theta
    coaster.append(3*vector(cos(theta),sin(theta),0))

while (theta <= 2*pi):
    theta += d_theta
    coaster.append(5*vector(cos(theta),sin(theta),0)+vector(0,2,0))

cart = sphere(pos=coaster.point(0).pos+vector(0.1,0.1,0),color=color.red,radius=0.1,speed=0,mass=1)
g = 1

But when I tried to run it in JupyterLab with the following code :

canvas()

coaster = curve(vector(-3,0,0),vector(-3,0,0))
theta = pi
d_theta = pi/100
while (theta <= 3*pi/2):
    theta += d_theta
    coaster.append(3*vector(cos(theta),sin(theta),0))

while (theta <= 2*pi):
    theta += d_theta
    coaster.append(5*vector(cos(theta),sin(theta),0)+vector(0,2,0))

cart = sphere(pos=coaster.point(0).pos+vector(0.1,0.1,0),color=color.red,radius=0.1,speed=0,mass=1)
g = 1

The coaster curve is drawn. But, the sphere did not appear because I got the following error : AttributeError: 'dict' object has no attribute 'pos'. Indeed, coaster.point(0) is a simple dictionary :

{'pos': vector(-3, 0, 0),
 'color': vector(1, 1, 1),
 'radius': 0,
 'visible': True,
 'retain': -1}

And pos is a key, not a property of an object.

For info, the vpython version is 7.6.5.

So, I wonder if it is possible to use the same code in a JupyterLab cell and at at glowscript.org ?