Changing text using Python

Solution 1:

Only use 1 fout.write(), call the replace function al often as you want.

with open("SanitizedFinal_E4300.txt", "rt") as fin:
    with open("output6.txt", "wt") as fout:
        for line in fin:
            line = line.replace('set system host-name EX4300', 'hostname "EX4300"')
            line = line.replace('set interfaces ge-0/0/0 unit 0 family inet address', 'ip address')
            fout.write(line)