I think it's this line that decides when it has reached one point, so that it can go onto the next. You're probably running into floating point issues. Maybe it needs to check with a tolerance.

I have the same problem:

bob = Turtle()
n = 7
ang = round(360/n, 1)
ds = 50
for i in range(2):
    bob.forward(ds)
    bob.left(ang)

does not work properly. The angle has just 1 decimal number, but the turtle does not draw the second line.

I think the turtle's angle changes in steps, and it overshoots the correct angle and then gets stuck turning one degree left and one degree right. Here's the code for that:

https://github.com/takluyver/mobilechelonian/blob/0.5/mobilechelonian/mobilechelonianjs/turtlewidget.js#L232-L248

Pull requests welcome :-)

I would like to speed up drawing circle
I use speed(10) method but not work.
As I know, drawing circle is using n-side line to finish this job
speed method only can help line section.
why?