What does .flush do? How can I change this to write to the file?

[snippsat]

Also for fun as this is written to be like tail -f which is command line tool.
Then can write to be a command line tool,eg i think Typer is cool.
So Typer is tool like eg argparse in standard library.

# py_tail.py
import typer
from collections import deque
import time

app = typer.Typer()

def follow_file(filename: str) -> None:
    with open(filename, 'r') as fh:
        # Go to the end of the file
        fh.seek(0, 2)
        while True:
            line = fh.readline()
            if not line:
                time.sleep(1)  # Wait a bit for new content
                continue
            print(line.rstrip('\n'))

@app.command()
def tail(
    filename: str,
    n: int = typer.Option(10, "--number", "-n", help="The last n lines of file"),
    follow: bool = typer.Option(False, "--follow", "-f", help="Show data as the file grows.")
    ):
    """
    Print the last n lines from a file. Optionally follow the file for new lines.
    """
    lines = deque(maxlen=n)
    try:
        with open(filename) as fh:
            for line in fh:
                lines.append(line.rstrip('\n'))
        for line in lines:
            print(line)
    except FileNotFoundError:
        typer.echo(f"File not found: {filename}")
        raise typer.Exit(code=1)
    if follow:
        follow_file(filename)

if __name__ == "__main__":
    app()

Now it's a command line tool and have also added eg tail -n 5 show the n lines of the file.
See that color is added automatic(it use Rich) which make it a good looking tool.