header in csv file printing every other line

I've been working this problem way too long, please explain to me why the header keeps repeating in my output csv.

I have an input csv with this data:

1. name,house
2. "Abbott, Hannah",Hufflepuff
3. "Bell, Katie",Gryffindor
4. "Bones, Susan",Hufflepuff
5. "Boot, Terry",Ravenclaw

The problem requires reversing last and first name, separate name into two columns, and make a new header with 3 columns for the output csv. Here's what I have:

    while True:
        try:
            # open file
            with open(sys.argv[1]) as file:
                # make reader
                reader = csv.reader(file)
                # skip first line (header row)
                next(reader)
                # for each row
                for row in reader:
                    # identify name
                    name = row[0]
                    # split at ,
                    name = name.split(", ")
                    # create var last and first, identify var house
                    last = name[0]
                    first = name[1]
                    house = row[1]


                    # writing the new csv
                    with open(sys.argv[2], "a") as after:
                        writer = csv.DictWriter(after, fieldnames=["first", "last", "house"])

                        # HEADER ONLY NEEDS TO OCCUR ONCE
                        writer.writeheader()
                        writer.writerow({"first": first, "last": last, "house": house})
                sys.exit(0)

my output csv:

1. first,last,house
2. Hannah,Abbott,Hufflepuff
3. first,last,house
4. Katie,Bell,Gryffindor
5. first,last,house
6. Susan,Bones,Hufflepuff

I've tried removing the while loop, unindenting and indenting, writing a row manually with the header names (which caused errors). Please help. Thanks!

source https://stackoverflow.com/questions/72340931/header-in-csv-file-printing-every-other-line