__main__.py

#!/usr/bin/env python3
"""Show number of bytes received."""
import socket
import sys
from concurrent.futures import ThreadPoolExecutor
from threading import Thread
from PyQt5.QtCore import pyqtSignal
from PyQt5.QtWidgets import QApplication, QLabel


def server(signal_obj, handler, *, host='localhost', port=29044,
           nconcurrent=40):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    # reuse sockets in TIME_WAIT state
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.bind((host, port))
    sock.listen()
    signal_obj.server_started.emit(host, port)
    with ThreadPoolExecutor(nconcurrent) as pool:
        while True:
            conn, addr = sock.accept()
            pool.submit(handler, conn).add_done_callback(
                lambda f: signal_obj.request_finished.emit(*addr, f.result()))


def count_nbytes(conn):
    """Count the number of received byte"""
    with conn:
        return sum(map(len, iter(lambda: conn.recv(8096), b'')))


class Widget(QLabel):
    server_started = pyqtSignal(str, int)  # host, port
    request_finished = pyqtSignal(str, int, object)   # *addr, result

    def display(self, *args):
        self.setText('Got: ' + ' '.join(map(str, args)))
        self.adjustSize()


app = QApplication(sys.argv)
w = Widget()
w.setWindowTitle('Count received bytes')
w.server_started.connect(w.display)
w.request_finished.connect(w.display)
w.show()
# run server in a background thread
Thread(target=server, args=[w, count_nbytes], daemon=True).start()
sys.exit(app.exec())