import selectors
import socket

mysel = selectors.DefaultSelector()
keep_running = True

def read(connection, mask):
    "Callback for read events"
    global keep_running

    client_address = connection.getpeername()
    print(‘read({})‘.format(client_address))
    data = connection.recv(1024)
    if data:
        # A readable client socket has data
        print(‘  received {!r}‘.format(data))
        connection.sendall(data)
    else:
        # Interpret empty result as closed connection
        print(‘  closing‘)
        mysel.unregister(connection)
        connection.close()
        # Tell the main loop to stop
        keep_running = False

def accept(sock, mask):
    "Callback for new connections"
    new_connection, addr = sock.accept()
    print(‘accept({})‘.format(addr))
    new_connection.setblocking(False)
    mysel.register(new_connection, selectors.EVENT_READ, read)

server_address = (‘localhost‘, 9999)
print(‘starting up on {} port {}‘.format(*server_address))
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.setblocking(False)
server.bind(server_address)
server.listen(5)

mysel.register(server, selectors.EVENT_READ, accept)

while keep_running:
    print(‘waiting for I/O‘)
    for key, mask in mysel.select(timeout=1):
        callback = key.data
        callback(key.fileobj, mask)

print(‘shutting down‘)
mysel.close()

import selectors
import socket

mysel = selectors.DefaultSelector()
keep_running = True
outgoing = [
    b‘It will be repeated.‘,
    b‘This is the message.  ‘,
]
bytes_sent = 0
bytes_received = 0

# Connecting is a blocking operation, so call setblocking()
# after it returns.
server_address = (‘localhost‘, 9999)
print(‘connecting to {} port {}‘.format(*server_address))
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect(server_address)
sock.setblocking(False)

# Set up the selector to watch for when the socket is ready
# to send data as well as when there is data to read.
mysel.register(
    sock,
    selectors.EVENT_READ | selectors.EVENT_WRITE,
)

while keep_running:
    print(‘waiting for I/O‘)
    for key, mask in mysel.select(timeout=1):
        connection = key.fileobj
        client_address = connection.getpeername()
        print(‘client({})‘.format(client_address))

        if mask & selectors.EVENT_READ:
            print(‘  ready to read‘)
            data = connection.recv(1024)
            if data:
                # A readable client socket has data
                print(‘  received {!r}‘.format(data))
                bytes_received += len(data)

            # Interpret empty result as closed connection,
            # and also close when we have received a copy
            # of all of the data sent.
            keep_running = not (
                data or
                (bytes_received and
                 (bytes_received == bytes_sent))
            )

        if mask & selectors.EVENT_WRITE:
            print(‘  ready to write‘)
            if not outgoing:
                # We are out of messages, so we no longer need to
                # write anything. Change our registration to let
                # us keep reading responses from the server.
                print(‘  switching to read-only‘)
                mysel.modify(sock, selectors.EVENT_READ)
            else:
                # Send the next message.
                next_msg = outgoing.pop()
                print(‘  sending {!r}‘.format(next_msg))
                sock.sendall(next_msg)
                bytes_sent += len(next_msg)

print(‘shutting down‘)
mysel.unregister(connection)
connection.close()
mysel.close()