function calls in init exit scope?

[Peter Ebus]

Hi everybody

I've been using vpython for a while to create visualisations for my electromagnetism class. Everything works fine when using vpython, but when I try to run code in Glowscript things stop working. I've been able to narrow it down to the following: It seems that calling functions during initialisation only runs the statement following the function call, then exits the method (see code example below). This seems to happen regardless of scope- I've tried making the function a member of the class, or even the init method itself, with the same result. As I'm no expert on Javascript I don't have a clue why this code works fine in vpython but does not compile to Javascript (or not as expected). Anyone know the reason for this behaviour, and possibly a solution? 

Thanks,

Peter

def red():
    return vec(1,0,0)

class Body:

    def __init__(self, a_pos, a_color):
        #self.my_color=red() # works as expected in vpython, but will only run next statement, then exit __init__() in Web VPython 3.2
        self.my_color = a_color
        self.my_pos = a_pos
        #self.my_color= red() # will not cause error, but will not update self.my_color

    def draw(self):
        arrow(pos=self.my_pos, axis=vec(-1, 0, 0), color=self.my_color)

my_body = Body(a_pos = vec(0, 0, 0), a_color=vec(0,1,0))
my_body.draw()

[Max DeMarr]

This is very funny behavior. When probing around at the timing of the current color value inside and outside of the class initialization, I found that it was starting the draw event with old values written to the color. Both of your commented-out lines are perfectly okay, but the draw method is being queued with the old value of the color. It seems that simply adding "sleep(0.01)" after you create the my_body instance of Body ensures that the values are properly updated. I am also not sure as to why this is needed.

Best,

- Maximillian

[Peter Ebus]

Hi Maximilian,

This does indeed confirm other behaviour I noticed earlier. Looks like instantiation starts a separate thread. sleep(0) after creating the instance does the trick. Ugly, but at least I have a workaround. Thanks for the update! 
Peter

[Harlan Gilbert]

This is part of a larger problem, as there are other behaviors where synchronization of functions is problematic.  (Rate statements in functions rather than the main program.)

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Harlan Gilbert, Ph.D.

High School Math, Physics, Computer Science, and Philosophy Teacher

Collegium Chair

Green Meadow Waldorf High School

Chestnut Ridge, NY 10977

(845) 356-2514 x. 320