Python port chooser

port.py

import socket

used_ports = [None]
def choose_port(address='127.0.0.1'):
    port = None
    while port in used_ports:
        testsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        testsocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        testsocket.bind((address, 0))
        port = testsocket.getsockname()[1]
        # testsocket.shutdown(socket.SHUT_RDWR) # seems to be unnecessary
        testsocket.close()
    used_ports.append(port)
    return port