ED3 DAT Pack v1

import os
import struct
import glob
import sys

hdr_index = []                          #Read the index file data
with open('hdrspec.csv','rb') as f:
    for line in f:
        line = line.translate(None,'\r\n')
        line = line.split(',')
        line[1] = int(line[1])
        hdr_index.append(line)

def dat_pack(filename):
    for filename1, hdrlen in hdr_index:     #Find header length
        if filename1 == filename + '.DAT':
            break
    else:
        print 'File not in index.'
        quit()

    with open(filename + '.DAT','wb') as f:     #Write new .DAT file
        f.write('LB DAT\x1A\x00')               #Secret code
        f.write(struct.pack('<I',hdrlen))       #Header length
        f.write('\x00'*4)                       #Format spec
        start_of_data = hdrlen*4 + 0x14         #Data start position
        pos = start_of_data                     #Position counter
        f.write(struct.pack('<I',start_of_data))    #Write 1st file location
        for f1 in glob.glob(filename + '\\' + '*.dat'): #Loop thru .dat files
            pos += os.path.getsize(f1)          #Increment position counter
            f.write(struct.pack('<I',pos))      #Write position of next file
        while f.tell() < start_of_data:         #Write 00 until start of data
            f.write('\x00'*4)
        for f1 in glob.glob(filename + '\\' + '*.dat'):     #Loop again
            with open(f1,'rb') as g:            #Write each file in succession
                f.write(g.read())

dat_pack(sys.argv[1])