Quick Tip: Kill a Runaway Python Process by Port in 3 Lines (No Task Manager)

Quick Tip

Every dev has hit this: you restart your dev server and get Address already in use. Something is squatting on port 8000 and lsof -i :8000 never sticks in my memory.

With psutil it's three lines and it works the same on macOS, Linux, and Windows:

import psutil

for conn in psutil.net_connections(kind="inet"):
    if conn.laddr.port == 8000 and conn.status == "LISTEN":
        print(f"PID {conn.pid} is holding :8000")
        psutil.Process(conn.pid).terminate()

No shell piping, no grep, no remembering whether this machine has lsof, netstat, or ss. Install with pip install psutil (that's the whole dependency tree).

I keep this as a killport.py in my dotfiles. Run it, port's free, dev server starts. I timed it against my usual lsof | grep | awk | kill dance — 4 seconds vs ~30 seconds of fumbling, every single time.

I sketched the snippet with an AI coding assistant (MonkeyCode, free tier: https://ly.cyberserval.tech/iIETXiF) and it nailed the net_connections API on the first try — including the Windows edge case where conn.pid can be None for system sockets.

What's the one tiny utility script you keep in your dotfiles that you'd fight someone over?