What is meant by "truncates the file" RE file.open(w+b)?

The default mode is 'r' (open for reading text, synonym of 'rt'). Modes 'w+' and 'w+b' open and truncate the file. Modes 'r+' and 'r+b' open the file with no truncation.
Which do I use if I want to seek within a file in binary mode, write to it in an overwrite rather than insertion mode, and close it?

edit

Also how would I convert a string "7F" or "1A" from a string representation of a hexadecimal number into a decimal number?

double edit

I think this should work for the last question.

int("7F",16)

int("1A",16)

int(lineList[3][n:n+1],16)

Here's the code for my script.

import sys,io

 

csvName = sys.argv[1]

with open(csvName, "r") as f:

    line = f.readline()

    while line != '':

        lineList = line.split(',')

        with open(lineList[0],"w+b") as writeFile:

            #waiting on python forum reply for above

            writeFile.seek(int(lineList[1]))

            #next do a loop where you grab lineList[3][n:n+1],

            #convert it from a hex string to an int,

            #and write it.

            #maybe int(lineList[3][n:n+1],16)

        line = f.readline()

         

        #file.seek(36,0)

        #address = file.read(1)[0]

        #address = ((file.read(1)[0] << 8) | address)

        #address = ((file.read(1)[0] << 16) | address)

        #address = ((file.read(1)[0] << 24) | address)

        #print(str(address))

        #print(hex(address))

#open csv file

#while (readfirstline() != EOF)

#{

#  split line along commas

#  open file in first element in array or list as write binary

#  seek to addresss in second element in array or list

#  convert third line into format writable to binary file

#  write third line

#  close file

#}

 

#just operating on one file, don't need this for loop or wildcards