Printing no output to a text file in python while reading specific lines

Question

I want to print every third line (starting from line 2) from a file to a new file. The example of the file ( line.txt ) is

line1
line2
line3
line4
line5
line6
line7
line8
line9
line10
line11

The output will be

line2
line5
line8
line11

The script that I have written is

with open ('line.txt') as file:
    for line in file.read().split("\n")[1::3]:
        print (line)
        f = open('output.txt','w')
        f.write(line)
        f.close()

But nothing is being copied in the output.txt file . The output.txt remains blank. Even if I print the line after running the script in python IDLE, the line returns blank ' '. But during running the script, the output is the desired output ie

line2
line5
line8
line11

Any help or tips would be greatly appreciated!

Answer 1

You are closing the output.txt file and opening it again every time in your loop. I would suggest to put these out of the loop:

with open('output.txt', 'w') as f:
    with open ('line.txt', 'r') as file:
        for line in file.readlines()[1::3]:
            print(line)
            f.write(line)

note: I also added +'\\n to the write statement to include line endings in your output.txt

Edit: as @DeepSpace rightly noted you could better use with open() for both files and readlines() instead of read().split('\\n') . Using with open() you don't need to remember to close it.

Answer 2

with open ('line.txt') as file:
        f = open('output.txt','w')
        for line in file.read().split("\n")[1::3]:
            outputline=line
            f.write(outputline)
        f.close()

Answer 3

the following script write in an file output.txt according your description I wish to print every third line (starting from line 2) from a file to a new file

output_file = open("output.txt", "a")
with open ('line.txt') as file:
    for line in file.readlines()[1::3]:
        output_file.write(line)
output_file.close()

I am using readlines() instead of read() becaute it reads a whole line instead of read a single string. Also I am using open file with "a" instead of "w" because the Appending mode allows you to append content in the file. With "w" you were overwriting each iteration of the loop. I hope it helps.