Building a Simple Python Port Scanner in 20 Lines

Port scanning is a practical technique used not only in information security but also in everyday operations, and implementing your own scanner in Python allows customization and addition of personal features.

Required libraries : The script uses only Python standard libraries—socket for low‑level network connections, argparse for command‑line argument parsing, sys for system interaction, and time for measuring execution duration.

Host argument : Using argparse, the script accepts a host name or IP address as the first positional argument, accessible via args.host .

Port scanning loop : It iterates over the full port range 1‑65535, creates a TCP socket for each port, sets a 1‑second timeout, and calls sock.connect_ex((args.host, port)) . If the result is 0, the port is reported as open; sockets are closed after each attempt. KeyboardInterrupt is caught to allow graceful termination.

Complete script :

import socket
import argparse
import sys
import time

parser = argparse.ArgumentParser()
parser.add_argument('host')
args = parser.parse_args()
start = time.time()

try:
    for port in range(1, 65536):
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.settimeout(1)
        result = sock.connect_ex((args.host, port))
        if result == 0:
            print("Port: {} Open".format(port))
        sock.close()
except KeyboardInterrupt:
    sys.exit()

end = time.time()
print(f"Scanning completed in: {end-start:.3f}s")

Running the script (which consists of exactly 20 lines of code) prints each open port and the total scanning time, as demonstrated by the accompanying screenshots.