如何从文本中检索“n”行？

Question

I am working with a FastQ file which is a text file with different elements in every 4 lines. I am trying to search for a certain string in a line and retrieve that line with the following three lines. But I am not sure how to do that. So far, I am only able to retrieve the target line, but not the following three. Supposing that my target line has a "XXXX" as part of the string, a fragment of my code is as follows:

with open (x, 'rt') as myfile:   
    for line in myfile:

        if re.findall ('.+XXXX.+', line):
            target.write (line)
            count_target = count_target + 1

        else:
            leftover.write (line)
            count_left = count_left + 1

How could I improve my code to get the four consecutive lines everytime it founds "XXXX"?

Answer 1

Once you found your line, call next(myfile) 3 times:

with open (x, 'rt') as myfile:   
    for line in myfile:

        if re.findall ('.+XXXX.+', line):
            target.write (line)
            for i in range(3):
                target.write(next(myfile))