Securely erases free disk space on small disks (flash drives, etc.)

shred.py

import os
import time

ITERATIONS = 3          # Number of passes
BLOCKSIZE = 1 << 20     # Bytes to be written at once
INFO_SECONDS = 3        # Interval in which output is displayed
FILE = 'crap'           # File where random output is dumped

def format_bytes(n):
    '''Human readable representation of bytes'''
    n = float(n)
    if n < 1024: return '%s Bytes' % n
    elif n < 1024 * 1024: return '%s KB' % round(n / 1024, 2)
    elif n < 1024 * 1024 * 1024: return '%s MB' % round(n / 1024 / 1024, 2)
    else: return '%s GB' % round(n / 1024 / 1024 / 1024, 2)

def print_info(bytes_written, bytes_recently, last_info_time):
    print "%s written at" % format_bytes(bytes_written),
    print "%s/s" % format_bytes(round(
            bytes_recently / (time.time() - last_info_time), 1))

def shred(iterations, filename, blocksize, info_seconds):
    for i in xrange(iterations):
        print "BEGIN: Pass %s of %s" % (i + 1, iterations)
        bytes_written = 0
        time_started = time.time()
        last_info_time = time.time()
        bytes_recently = 0
        
        with file(filename, 'wb') as f:
            while 1:
                try:
                    f.write(os.urandom(blocksize))
                except KeyboardInterrupt:
                    return
                except:
                    print "DONE: Pass %s of %s" % (i + 1, iterations)
                    break

                bytes_written += blocksize
                bytes_recently += blocksize
                    
                if time.time() - last_info_time >= info_seconds:    
                    print_info(bytes_written, bytes_recently, last_info_time)
                    last_info_time = time.time()
                    bytes_recently = 0
    
            
if __name__ == '__main__':
    shred(ITERATIONS, FILE, BLOCKSIZE, INFO_SECONDS)
    os.remove(FILE)