BS-X SRAM Checksum Fixer

from struct import *
import sys
print "BS-X SRAM Checksum Fixer v0.2"
print "By LuigiBlood/Seru-kun"
#Usage: CHKFIX.py [-f] <SRAM File>
#  -f = Fix Checksum

#12287
if sys.argv[1] == "-f" and sys.argv[2] <> "" :
   FILE = sys.argv[2]
elif sys.argv[1] <> "-f" and sys.argv[1] <> "" :
   FILE = sys.argv[1]

if FILE <> "" and sys.argv[1] == FILE :
   SRAM = open(FILE,"r+b")
   CHK = 0
   CHK2 = 0
   OFFSET = int("2fff", 16)
   SRAM.seek(4)
   OLD=ord(SRAM.read(1))+ord(SRAM.read(1))*256
   print "Checksum : " + hex(OLD)
   SRAM.seek(2)
   OLDR=ord(SRAM.read(1))+ord(SRAM.read(1))*256
   print "Reversed Checksum : " + hex(OLDR)
elif FILE <> "" and sys.argv[1] == "-f" and sys.argv[2] == FILE :
   SRAM = open(FILE,"r+b")
   CHK = 0
   CHK2 = 0
   A = 0
   OFFSET = int("fff", 16)
   SRAM.seek(4)
   OLD=ord(SRAM.read(1))+ord(SRAM.read(1))*256
   print "Checksum : " + hex(OLD)
   SRAM.seek(2)
   OLDR=ord(SRAM.read(1))+ord(SRAM.read(1))*256
   print "Reversed Checksum : " + hex(OLDR)
   SRAM.seek(2)
   SRAM.write(chr(255))
   SRAM.write(chr(255))
   SRAM.write(chr(0))
   SRAM.write(chr(0))
   print "Checksum Removed, calculating..."
   while OFFSET >= 0:
       SRAM.seek(OFFSET)
       A = ord(SRAM.read(1))
       A += CHK
       CHK = A
       SRAM.seek(OFFSET + int("1000", 16))
       A = ord(SRAM.read(1))
       A += CHK
       CHK = A
       SRAM.seek(OFFSET + int("2000", 16))
       A = ord(SRAM.read(1))
       A += CHK
       CHK = A
       OFFSET -= 1

   SRAM.seek(2)
   CHK2 = CHK & int("ffff", 16)
   print "NEW Checksum : " + hex(CHK2)
   RCHK = CHK2 ^ int("ffff", 16)
   print "NEW Reversed Checksum : " + hex(RCHK)
   print "Replacing Checksums..."
   SRAM.write(pack("H", RCHK))
   SRAM.write(pack("H", CHK2))
   print "Done !"