The interpreter doesn't realize that print () is part of that loop. Try not sending EOT on the for loop line. If that works, you're going to need to implement a parser that detects if the next line ...

for line in sys.stdin.readlines(): fields = line.split("\t") for field in fields[:250]: file1.write(field + '\t') file1.write('\n') It's just taking the first 250 elements of a list and writing them ...