Nayuta Text Decompress v2

import os
import struct

def get_data(filename):
    totalbytes = os.path.getsize(filename)
    infile = open(filename, 'rb')
    totalfiledata = infile.read(totalbytes)
    infile.close()
    return totalfiledata

def replacestr(origstr,replacestr,startpos,replacelen):
#Returns a string with a replaced sub-string
#origstr - the original string, replacestr = the string to replace
#startpos - where the replacement string should go
#replacelen - how many characters of the original string to replace
    return origstr[:startpos] + replacestr + origstr[startpos+replacelen:]

def myprogram(filename,messageoffset):
    filedata = get_data(filename + '.orig')
    unknown_data1 = filedata[:messageoffset]
    unpacked_size = struct.unpack('<I',filedata[messageoffset+4:messageoffset+8])[0]
    number_of_chunks = struct.unpack('<I',filedata[messageoffset+8:messageoffset+12])[0]
    unknown_data2 = filedata[-8:]
    filedata = get_data(filename  + '.unpack3')
    pos = 0
    output = []
    print '{:8} {}'.format(filename, number_of_chunks)

    for chunk in range(number_of_chunks):
        if chunk == number_of_chunks - 1:
            output.append(unknown_data2)
            break
        output2 = ['\x00']
        bits = 8
        flag = False
        if len(filedata) - pos >= 0x7FF0:
            chunk_end = 0x7FF0 * (chunk + 1)
        else:
            chunk_end = len(filedata)
        startpos = pos
        while pos < chunk_end:
            if bits == 0:
                if chunk_end - pos < 16:
                    flag = True
                    s = '0'*(14 - (chunk_end - pos)) + '11' + '0'*(chunk_end - pos)
                    print '{:8} {} {}'.format(filename, chunk, s)
                    output2.append(struct.pack('>H',int(s,2)))
                else:
                    output2.append('\x00'*2)
                bits = 16
            output2.append(filedata[pos])
            bits -= 1
            pos += 1
        if flag:
            output2.append('\x00')
        else:
            s = '0'*14 + '11'
            output2.append(struct.pack('>H',int(s,2)))
            output2.append('\x00')
        if chunk != 0:
            output.append('\x01')
        output.append(struct.pack('<H',len(''.join(output2)) + 3)) #Chunk size, 3 = size plus 00 byte
        output.append('\x00')
        output += output2

    newlen = len("".join(output)) + 8 #8 = 4 bytes for unpacked size, 4 bytes for # of chunks
    outfile = open(filename + '.tbb','wb')
    outfile.write("".join([unknown_data1, #Data before the message
                           struct.pack('<I',newlen), #Message size
                           struct.pack('<I',unpacked_size),
                           struct.pack('<I',number_of_chunks)]))
    outfile.write(''.join(output))
    outfile.close()

    filedata = get_data('data.lst')
    basepos = 0x14150
    newsize = os.path.getsize(filename + '.tbb')
    pos = filedata.find(filename + '\x00'*(8-len(filename)),basepos)
    if pos == -1:
        print 'Error'
        quit()
    filedata = replacestr(filedata,struct.pack('<I',newsize),pos+8,4)
    outfile = open('data.lst','wb')
    outfile.write(filedata)
    outfile.close()

myprogram('monslib',0x1F)
myprogram('questlib',0x1F)
myprogram('fldlist0',0x1F)
myprogram('fldlist1',0x1F)
myprogram('fldlist2',0x1F)
myprogram('fldlist3',0x1F)
myprogram('helplib',0x1F)
myprogram('foodarea',0x1F)