python buffering in sys.stdout

Minimal example:

def main():
    for i in range(100):
        print("One line every 2s", end = "\n")
        time.sleep(2)
if __name__ == '__main__':
    with open("log.out", 'w') as out, open("log.err", 'w') as err:
        sys.stdout = out
        sys.stderr = err
        main()

I want the print statements to be written toe the stdout file after every line. I tried unsuccesfully:

python -u thisfile.py

In the bashrc (zshrc)

PYTHONUNBUFFERED = 1 

open("log.out", 'wb', buffering = 0) 

Changing the main function is no an option for the real case. A solution where I run the python file with bash and redirect errors and output is ok tough.

I know theres lots of questions like this, but none seem to work for me.

The solution should work ideally for python 3.8 and anything newer.

You can use the subprocess module to run the script with the desired options and redirect the output and error streams to the log files:

import subprocess

with open("log.out", "w") as out, open("log.err", "w") as err:
    subprocess.run(["python", "-u", "thisfile.py"], stdout=out, stderr=err)

This will run the script in unbuffered mode (-u option) and redirect the output and error streams to the specified log files.