Вопрос Python 2.6.Ошибка. Invalid Syntax.ошибка в elif.Какая?

import mcpi.minecraft as minecraft
import mcpi.block as block
import time
mc = minecraft.Minecraft.create()
bridge = []
def buildBridge():
pos = mc.player.getTilePos()
b = mc.getBlock(pos.x, pos.y-1, pos.z)
if b == block.AIR.id or b == block.WATER_STATIONARY.id or b == block.WATER_FLOWING.id:
mc.setBlock(pos.x, pos.y-1, pos.z, block.GLASS.id)
coordinate = [pos.x, pos.y-1, pos.z]
bridge.append(coordinate)
elif b != block.GLASS.id:
if len(bridge) > 0:
coordinate = bridge.pop()
mc.setBlock(coordinate[0], coordinate[1], coordinate[2], block.AIR.id)
time.sleep(0.25)
while True:
time.sleep(0)
buildBridge()

ошибка в elif.Какая?