Easily corrupt any file

corrupt.py

import sys, random

if not len ( sys.argv ) > 2 :
    print 'Usage: python ' + sys.argv[0] + ' seed,amount[,variant] infile [corrupted]'
    exit ( 1 )

original = sys.argv[2]

# Parse the parameters
params = sys.argv[1].split ( ',' )
if len ( params ) == 2:
    ( seed, amount ) = params
    variant = 0
elif len ( params ) == 3:
    ( seed, amount, variant ) = params

try:
    seed = int ( seed )
    amount = int ( amount )
    variant = int ( variant )
except ValueError:
    print 'seed, amount and variant must be integers'
    exit ( 1 )

# Seed the RNG
random.seed ( seed )

# Open the file and read it into memory as a mutable byte array
with open ( original, 'rb' ) as f :
    b = bytearray ( f.read() )

# Make sure that we don't select more bytes than we have
amount = min ( len ( b ), amount )

# Select the bytes to be corrupted
victims = random.sample ( xrange ( len ( b ) ), amount )

# Corrupt 'em
for v in victims :
    b[v] = chr ( ( random.randint ( 0, 255 ) + variant ) % 0x100 )

# Generate the filename or use the one provided
outfile = sys.argv[3] if len ( sys.argv ) >= 4 else sys.argv[2] + '.' + str ( seed ) + '-' + str ( amount ) + '-' + str( variant ) + '.corrupted'

# Write out the corrupted file
with open ( outfile, 'wb' ) as output :
    output.write ( b )