Problem with Python objects

[Gilles Dubois]

The following program :

from vpython import *

scene.background=color.white*0.7
class revo:
    n=100
    da=2
    a=da*pi/180
    def norma(L):
        s = vec(0, 0, 0)
        for v in L:
            s = s + v
        return s / len(L)
    def __init__(self,min,max,f,col,op):
        self.xmin=min
        self.xmax=max
        self.fonc=f
        self.couleur=col
        self.opacity=op
        self.step=(max-min)/revo.n
    def P2D (self):
        return [(self.xmin + i * self.step, self.fonc(self.xmin + i * self.step)) for i in range(revo.n + 1)]

    def Vertices(self):
        Vert=[]
        for i in range(0, int(360 / revo.da)):
            V = [vertex(pos=vec(x[0], x[1], 0), normal=vec(0, 0, 1)) for x in self.P2D()]
            for v in V:
                v.rotate(axis=vec(0, 1, 0), angle=revo.a * i, origin=vec(0, 0, 0))
            Vert.append(V)
        V = [vertex(pos=vec(x[0], x[1], 0), normal=vec(0, 0, 1)) for x in self.P2D()]
        Vert.append(V)
        return Vert
    def Quads(self):
        LQ = []
        SV=self.Vertices()
        for k in range(0, int(360 / revo.da)):
            V1 = SV[k]
            V2 = SV[k + 1]
            for i in range(revo.n):
                s1 = V1[i]
                s2 = V1[i + 1]
                s3 = V2[i + 1]
                s4 = V2[i]
                LP = [s1.pos, s2.pos, s3.pos, s4.pos]
                N = revo.norma(LP)
                s1.normal = N
                s2.normal = N
                s3.normal = N
                s4.normal = N
                LQ.append(quad(vs=[s1, s2, s3, s4]))
        return LQ
    def nappe(self):
        scene.visible=False
        R = compound(self.Quads())
        R.color = self.couleur
        R.opacity = self.opacity
        scene.visible=True
        return R


def g(x):
    return x*x

R=revo(0,5,g,color.green,0.5)
scene.visible=True
REV=R.nappe()

works very well with installed python and Pycharm editor and represents the surface generated by a curve  y=f(x) turning around the y axis. (here a simple parabola y=x^2)

Now if I try it with Trinket

link 

I have the error message 

Unexpected identifier 'self'

The same with web vpython, without any line number

If somebody can explain.

T

[Steve Spicklemire]

Thanks Gilles,

I can’t exactly explain, but I think I may have discovered the basic problem.

I’ll say two things. First, I think this conversation probably belongs in the WebVPython group, since it’s really a WebVPython issue, so it might be helpful to raise it there. Second, I found a much simpler way to trigger the same issue:

------------------
Web VPython 3.2

def foo(x):
return 2*x

class bar:
def __init__(self, f):
self.f = f

def baz(self, check):
if check:
for x in range(2):
print(self.f(x))
# else:
# print([self.f(x) for x in range(2)])

b = bar(foo)

b.baz(True)
———————

If you uncomment the “else” clause in the “baz” method you’ll get the same error. I think it somehow arises because of the list comprehension mixed with a function object set as an attribute of the bar instance. I’ll dig into it a bit more when I get a chance. Thanks for the report!

-steve

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[Gilles Dubois]

In addition, making some tests I discovered that Web vpython wasn't comfortable with anonymous functions

This :

Web VPython 3.2 
g=lambda x:x*x
print(g(2))

doesn't work

but this 

Web VPython 3.2 WASM
g=lambda x:x*x
print(g(2))

is OK !
I discovered it trying to pass such a function as an argument to my revo object constructor

Now if we come back to the comprehension list issue.

This feature is very important for me 

it's elegant, readable, efficient, natural very close to the usual mathematical definitions of sets. It's a pity to use a for .. loop instead 

[Gilles Dubois]

I completed the initial program with some widgets just to test

link

With Pycharm and Python installed color change and start/stop both work. 

Slider to change the function from x*x to A*x*x  doesn't work with ANY version (without any error message.)

With web python WASM it is even completely disabled and in addition start/stop button doesn't work (again without any error mention)

[Gilles Dubois]

Last version
The program works with python 3.12 installed and Pycharm editor

Under web vpython WASM after first trial of the slider the program is entirely frozen.