from mcpi.minecraft import Minecraft
mc = Minecraft.create()
import time

x = -20
y = 52
z = -7


while True:
    gift = mc.getBlock(x, y, z)
    if gift == 57:
        mc.setBlock(-3, 50, 4, 152)
    elif gift != 0:
        mc.postToChat("Access Denied!")
        time.sleep(1.5)
    else:
        mc.setBlock(-3, 50, 4, 0)