error 'ring' is not a callable object

[nilamo]

    ring = ring(pos=s,axis=v,radius=1.0,color=color.red)

You're getting one ring, and then an error, because the first time through the loop you call ring()... and then overwrite the "ring" function by assigning something to the variable. Rename your variable (or just don't assign ring()'s output, since you don't use it anyway), and it might work.