import selectorsimport socket sel = selectors.DefaultSelector() def accept(sock, mask):    conn, addr = sock.accept()  # Should be ready    print('accepted', conn, 'from', addr)    conn.setblocking(False)    sel.register(conn, selectors.EVENT_READ, read) def read(conn, mask):    data = conn.recv(1000)  # Should be ready    if data:        print('echoing', repr(data), 'to', conn)        conn.send(data)  # Hope it won't block    else:        print('closing', conn)        sel.unregister(conn)        conn.close() sock = socket.socket()sock.bind(('localhost', 10000))sock.listen(100)sock.setblocking(False)sel.register(sock, selectors.EVENT_READ, accept) while True:    events = sel.select()    for key, mask in events:        callback = key.data        callback(key.fileobj, mask)