Read lines until a particular line occurs

Your code has a few problems including referring to a variable x1 that hasn't been defined, and defining count and i variables that aren't used. Trying to get content_file.next() won't work, because you already read all the content when you called content_file.readlines().

Instead do something like this: iterate through the content; if a line contains a title then set a flag and write the line to the output file; the flag will be True, and the loop will keep writing lines, until it encounters 'end'.

with open('titles', 'r') as titles_file:
    titles = [title.strip().upper() for title in titles_file]
description = False
with open('H:/Python/proj1/p4 faults.swi', 'r') as content, open('outfile.txt') as output:
    for line in content:
        if description:
            output.write(line)
            if line.strip().upper() == "END":
                 description = False
        elif line.strip().upper() in titles:
            output.write(line)
            description = True