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

[MysticLord]

https://docs.python.org/3/library/functions.html#open

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