#!/usr/bin/python3
# written by andrewtunsw.edu.au as a COMP(2041|9044) lecture example

# For each file given as argument replace occurrences of Hermione
# allowing for some misspellings with Harry and vice-versa.
# Relies on Zaphod not occurring in the text.

import re, sys, os

for filename in sys.argv[1:]:
    tmp_filename = filename + ".new"
    if os.path.exists(tmp_filename):
        print(f"{sys.argv[0]}: {tmp_filename} already exists\n", file=sys.stderr)
        sys.exit(1)
    with open(filename) as f:
        with open(tmp_filename, "w") as g:
            for line in f:
                changed_line = re.sub(r"Herm[io]+ne", "Zaphod", line)
                changed_line = changed_line.replace("Harry", "Hermione")
                changed_line = changed_line.replace("Zaphod", "Harry")
                g.write(changed_line)
    os.rename(tmp_filename, filename)