Falling simulation

from pymclevel import MCSchematic
from pymclevel import TileEntity
from pymclevel import TAG_Compound
from pymclevel import TAG_Short
from pymclevel import TAG_Byte
from pymclevel import TAG_String
import random

displayName = "Falling simulation"
def perform(level, box, options):
    blocks = []
    for x in xrange(box.minx, box.maxx):
        for z in xrange(box.minz, box.maxz):
            for y in xrange(box.miny, box.maxy):
                if level.blockAt(x, y, z) != 0:
                    blocks.append(level.blockAt(x, y, z))
            i = 0
            for yb in xrange(box.miny, box.maxy):
                if i < len(blocks):
                    level.setBlockAt(x, yb, z, blocks[i])
                    i+=1
                else:
                    level.setBlockAt(x, yb, z, 0)
            blocks = []
    level.markDirtyBox(box)