Help with python code to search string in one file & replace with line in other file

[Larz60+]

I'm not going to get to this tonight, but will pick it up first thing in the AM.
I'll post the code if you want to play with it before then.
It's now replacing all of the headers, and not the data, but it's reusing the same header lines from file2.
I think I know why, but need to spend some time with my wife.
I'll pick it up latter tonight or in the A.M. (EST)

I named the program MyParse.py, you can call it whatever you like, but just change the run command which is:

MyParse.py -i 'File1.txt' -b 'File2.txt' -o 'Fileout.txt'

here's the code:

# Replace header inoriginal file header with header in header file, writing output to outputfile
# Larz60+
from pathlib import Path
import argparse

class SwapHeaders:
    def __init__(self, origfile=None, headerfile=None, outfile=None):
        self.home = Path('.')
        self.data = self.home / 'data'
        self.original_file = self.data / origfile
        self.header_file = self.data / headerfile
        self.out_file = self.data / outfile

        with self.header_file.open() as fh:
            self.header_data = fh.readlines()

        self.orig = self.original_file.open()
        self.fo = self.out_file.open('w')

    def close_files(self):
        self.orig.close()
        self.fo.close()

    def get_replacement_header(self, match):
        retrec = None
        for line in self.header_data:
            if not line.startswith('>'):
                continue
            if match in line:
                retrec = line
                break
        return retrec

    def read_orig_record(self):
        """
        original file record read
        :return: data or False
        """
        while True:
            data = self.orig.readline()
            if not data:
                break
            yield data

    def make_new_file(self):
        with self.out_file.open('w') as fo:
            for orig in self.read_orig_record():
                if orig.startswith('>'):
                    match = orig[1:]
                    x = match.rfind('.')
                    if x:
                        match = match[:x]
                    new = self.get_replacement_header(match)
                    if new is not None:
                        fo.write(new)
                    else:
                        fo.write(orig)
                else:
                    fo.write(orig)

def main():
    # Typical command line call python MyParse.py -i 'File1.txt' -b 'File2.txt' -o 'Fileout.txt'
    parser = argparse.ArgumentParser()
    parser.add_argument("-i", "--ifile",
                        dest='original_filename',
                        help="Filename where headers are to be replaced",
                        action="store")

    parser.add_argument("-b", "--bfile",
                        dest='replace_original_filename',
                        help="Filename containing body",
                        action="store")

    parser.add_argument("-o", "--ofile",
                        dest='out_filename',
                        help="Output filename",
                        action="store")

    args = parser.parse_args()
    original_filename = args.original_filename

    replace_original_filename = args.replace_original_filename

    out_filename = args.out_filename

    sh = SwapHeaders(origfile=original_filename, headerfile=replace_original_filename, outfile=out_filename)
    sh.make_new_file()
    sh.close_files()

if __name__ == '__main__':
    main()