Wander Wonder .FLD Pack v1

import os
import struct
import glob
specfile = 'fldfilespec.csv'    #Define constant value
specpath = 'fldpathspec.csv'    #Define constant value

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

#This is the workhorse function. Like the name says, it packs up an FLD file.
def fld_pack(targetfile):
    for filename, filelist in filespec: #From the filespec data, finds the file list.
        if filename == targetfile:      #Breaks out of the loop when correct file is found
            break
    for filename, path in pathspec:     #From the pathspec data, find the path.
        if filename == targetfile:      #Breaks out of the loop when correct file is found
            break
    with open(targetfile,'wb') as f:
        f.write('FLDF0200')             #Super-special secret code
#The start of the index table is computed by:
#0x14 (where the path info would go) + length of the path string + 1
#The 1 is added because there MUST be at least one null byte following the path string
#After this value is computed, it needs to be 4-byte aligned
        tablestart = 0x14 + len(path) + 1   #Find start of the index table
        while tablestart % 4 != 0:          #4-byte align the index table start value
            tablestart += 1
        f.write(struct.pack('<I',tablestart))   #Write the index table start position because it's part of the FLD file spec
        f.write(struct.pack('<I',len(filelist)))    #Write how many files are in this .fld file
        f.write('\x00'*4)                       #Write four null bytes because it's part of the FLD file spec
        f.write(path)                           #Write the path info
        while f.tell() != tablestart:           #Pad out the path info with nulls until the start of the index table
            f.write('\x00')
#The position of the start of the file data is computed by:
#Start of the index table + [number of files] * 0x14
#This is because, in the index table, the entry for each file is 0x14 long
        datapos = tablestart + len(filelist)*0x14   #Compute the position where the file data starts
        for filename in filelist:               #Loop over the file list
            f.write(filename + '\x00'*(12-len(filename)))   #Write the filename
            f.write(struct.pack('<I',datapos))              #Write where in the file the filename goes
            fsize = os.path.getsize(path + filename)        #Find how big the file is
            f.write(struct.pack('<I',fsize))                #Write the file size
            datapos += fsize                                #Compute position of next file
        for filename in filelist:               #Loop over the file list AGAIN
            f.write(get_data(path + filename))  #Write the data for each file to the end

global filespec, pathspec   #I made these globals so the workhorse function can access their values
filespec = []               #Initialize variables
pathspec = []
with open(specfile) as f:   #Read in the SPECFILE file
    filename = ''
    for line in f:
        line = line.translate(None,'\r\n')  #Delete line break characters at end of line
        line = line.split(',')              #Make a list, splitting along the comma
        if line[0] == filename:             #If the filename is the same as the previous line
            filespec[-1][-1].append(line[1])    #Append the sub-file name to the file list
        else:                               #If the filename is different than the previous line
            filespec.append([line[0],[line[1]]])    #Append a new entry to the list
            filename = line[0]                      #Update 'current' filename
with open(specpath) as f:   #Read in the SPECPATH file
    for line in f:
        line = line.translate(None,'\r\n')  #Delete line break characters at end of line
        pathspec.append(line.split(','))    #Append the filename and path to the list

for fldfile in filespec[0][1]:  #Loop over the file list for wander.fld
    fld_pack(fldfile)           #Pack each sub-fld file
fld_pack('wander.fld')          #Then pack wander.fld itself