for y, d in [(bb1[1], -3), (bb2[1], 3)]:
p1 = scale*Numeric.array([lower, y])+shift
p2 = scale*Numeric.array([upper, y])+shift
for y, d in [(bb1[1], -3), (bb2[1], 3)]:
p1 = scale*Numeric.array([lower, y])+shift
p2 = scale*Numeric.array([upper, y])+shift