Rot13 Python Script (Useful Enough For Me)

#!/usr/bin/python3
import os
import sys
import codecs

def rot(msg):
    return codecs.encode(msg, "rot13")

def parse_arguments():
    infile = None
    outfile = None
    log_to_terminal = True
    msg = ""
    for i, arg in enumerate(sys.argv[1:]):
        if arg == "-i": #input file
            msg += open(sys.argv[i+2], "r").read() + "\n"
        elif arg == "-s": #silent
            log_to_terminal = False
        elif arg == "-t": #input text
            msg += sys.argv[i+2] + "\n"
        elif arg == "-o": #output file
            outfile = sys.argv[i+2]
    if msg == "":
        print("No text was entered to be encoded. Please add text using -t \"text\" or -i \"/path/to/file\"")
    return infile, outfile, log_to_terminal, msg

def main(infile, outfile, log_to_terminal, msg):
    if not infile == None:
        msg = open(infile, "r").read()
    out = rot(msg)
    if log_to_terminal:
        print(out);
    if not outfile == None:
        file = open(outfile, "w")
        file.write(out)
        file.close()

if __name__ == "__main__":
    if "--help" in sys.argv:
        print("""Usage: ./script.py [-option] [data]\n  -i input file path\n  -s do not print output in terminal\n  -t input text\n  -o output to file path\n\nMultiple -t and -i options can be used. Each instance will be seperated by a new line.""")
        exit()
    infile, outfile, log_to_terminal, msg = parse_arguments()
    main(infile, outfile, log_to_terminal, msg)