Will this bitscrubber in fact scrub away bits rather than writing to a new file?

Question

I have a Unix-y bash script and a Python script:

#!/bin/bash
for item in $*
do
    for file in `find $item -type f`
    do
        bitscrubber_internal $item
    done
    rm -rf $item
done

and

#!/usr/bin/python

import sys

filename = sys.argv[1]

length = len(open(filename).read())

for number in [0x0, 0xff, 0xf0, 0x0f]:
    open(filename, 'wb').write(('%f' % number) * length)

I know this will run into preventable scaling issues if it encounters a file that won't fit in memory, but apart from that, will this scrub over the same bits in the file, or create a new file which scrubs old blocks only by coincidence? I am running Lion.