How do I write a single 8-bit byte to a file?

[MysticLord]

Thanks, it works.

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],"r+b") as writeFile:
            writeFile.seek(int(lineList[1]))
            writeFile.write(bytes.fromhex(lineList[2]))
        line = f.readline()