Tail last N lines of growing log file in Python

import time
from pathlib import Path

def tail_log(file_path, n=10, poll_interval=1.0, timeout=10):
    """
    Print the last n lines and follow new lines appended to a growing log file.
    """
    path = Path(file_path)
    # Read the last n lines from the current file
    with path.open("r", encoding="utf-8") as f:
        lines = f.readlines()[-n:]
    print("".join(lines), end="")

    # Track file size and follow new content
    size = path.stat().st_size
    end_time = time.time() + timeout
    while time.time() < end_time:
        current_size = path.stat().st_size
        if current_size > size:
            with path.open("r", encoding="utf-8") as f:
                f.seek(size)
                new_data = f.read()
                if new_data:
                    print(new_data, end="")
                size = f.tell()
        time.sleep(poll_interval)

if __name__ == "__main__":
    # Demo: create a temp log, append lines, and tail it
    import tempfile
    log_path = Path(tempfile.gettempdir()) / "demo_tail.log"
    log_path.write_text("line1\nline2\nline3\nline4\nline5\n")

    tail_log(log_path, n=3, timeout=3)

    # Simulate growth in a background thread
    import threading
    def grow():
        time.sleep(1)
        with log_path.open("a") as f:
            f.write("line6\nline7\n")
    threading.Thread(target=grow, daemon=True).start()