from mcpi.minecraft import Minecraft
mc=Minecraft.create()
x,y,z=mc.player.getTilePos()
for i in range(20):
    mc.setBlock(x+i,y-1,z-i,47)
    mc.setBlock(x+i+1,y-1,z-i,47)  
    mc.setBlock(x+i+2,y-1,z-i,47)