srt file + txt file => srt file with all text replaced

subtitle-replace.py

#!/usr/bin/env python3

import argparse, re, sys

parser = argparse.ArgumentParser(
    description='replace subtitle text with corrected text',
    formatter_class=argparse.ArgumentDefaultsHelpFormatter)
parser.add_argument('sub', help='subtitle file')
parser.add_argument('txt', help='corrected text file')
args = parser.parse_args()

timestamp = re.compile(r'^\d{2}:\d{2}:\d{2},\d{3} --> ')

srt = open(args.sub, encoding='utf-8')
txt = open(args.txt, encoding='utf-8')
for line in srt:
    if timestamp.match(line):
        # Print timestamp
        sys.stdout.write(line)

        # Replace all subtitle text lines until the blank line
        while True:
            line = next(srt)
            if line.strip() == '':
                sys.stdout.write('\n')
                break
            sys.stdout.write(next(txt))
    else:
        # Subtitle number or blank line
        sys.stdout.write(line)
srt.close()
txt.close()