import socket
import selectors
import sys
import io


selector = selectors.DefaultSelector()

def server():

    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server_socket.bind(('localhost', 5000))
    server_socket.listen()

    selector.registet(fileobj=server_socket, events=selectors.EVENT_READ,
    data=accept_connection)

def accept_connection(server_socket):

    client_socket, addr = server_socket.accept()
    print('Connection from', addr)

    selector.registet(fileobj=server_socket, events=selectors.EVENT_READ,
    data=send_message)


def send_message(client_socket):

    request = client_socket.recv(4096)

    if request:
        response = 'Pong\n'.encode()
        client_socket.send(response)
    else:
        selector.unregister(client_socket)
        client_socket.close()


def event_loop():

    while True:

        events = selector.select()  # (key, events)

        # SelectorKey
        # fileobj
        # events
        # data

        for key, _ in events:
            callback = key.data
            callback(key.fileobj)


if __name__ == '__main__':

    server()
    event_loop()