Develop Reference

Only one user can connect to websocket server with tornado at a time

I am trying to develop a websocket server with Python and tornado. This websocket server streams a large database result to the client for some visualization.
The problem that I am facing is that no client can connect until the long process (send_data) is finished. It is as if only one client can connect at a time.
Is websocket already an async process or should I implement an async process?
The following is my code:
import time
import random
import json
import datetime
import os
import sys
import cx_Oracle
import string
import re
import subprocess
import asyncio
from tornado import websocket, web, ioloop, escape
from datetime import timedelta
from random import randint
from pprint import pprint
from tornado.web import RequestHandler
os.environ['ORACLE_HOME'] = 'pathToOracleHome'
os.environ['LD_LIBRARY_PATH'] = "$ORACLE_HOME/lib"
def is_hex(a):
printable = set(string.printable) - set("\x0b\x0c")
return any(c not in printable for c in a)
def json_print(d):
print(json.dumps(d, indent=4))
def printf (format,*args):
sys.stdout.write (format % args)
def db(database_name='localhost/database'):
return cx_Oracle.connect('user', 'pwd', database_name)
def query_db(query, args=(), one=False):
cur = db().cursor()
cur.arraysize = 1500
cur.execute(query, args)
return cur
class SummaryWebSocketHandler(websocket.WebSocketHandler):
clients = []
def check_origin(self, origin):
return True
def on_message(self, message):
print ('message received')
def closeDbConn(self,cur):
cur.connection.close()
def query(self, sql):
cursor = query_db(sql)
self.send_data(cursor)
### THIS IS THE LONG PROCESS ###
def send_data(self, cur):
results = {}
columns = [column[0] for column in cur.description]
total = 0
while True:
Res = []
rows = cur.fetchmany()
if rows == []:
print('no more rows')
break;
for row in rows:
results = {}
for i, value in enumerate(row):
if value == None:
value = '-'
results[cur.description[i][0]] = value
Res.append(results)
self.write_message(json.dumps(Res))
total = total + len(rows)
print('total rows send', total)
self.write_message("finished sending all data")
self.on_close(cur)
def open(self, table):
print ('Connection established. \n')
print ('Query string '+table+'\n')
p = re.compile(r'fields=')
m = p.match(table)
matches = table.split("&")
print (matches)
param_string = ''
params = []
if matches:
for m in matches:
print('m', m);
param = ''
items = m.split('=')
if items[1] != '':
param = '--'+items[0]+' '+items[1]
params.append(param)
param_string = " ".join(params)
script = "php getStmt.php "+param_string
print (script)
proc = subprocess.Popen(script, shell=True,stdout=subprocess.PIPE)
sql = proc.stdout.read()
print (sql)
self.query(sql)
def on_close(self, cursor):
print ('Connection closed.')
cursor.close()
settings = {'auto_reload': True, 'debug': True}
if __name__ == "__main__":
print ("Starting websocket server program. Awaiting client requests to open websocket ...")
application = web.Application([(r"/\/table\/(.*)",SummaryWebSocketHandler),
]
,**settings)
application.listen(3001)
ioloop.IOLoop.instance().start()

How do I use multiple threads with PySide and Twython?

I'm trying to write a small python app, using PySide for the GUI and Twython as a Twitter API library, to catch a stream from Twitter.
The problem that I am having is that when I click "Start Monitoring Twitter" button, the UI freezes until the stream is complete, at which point the code continues to execute and disables the Start button and enables the Stop button. Here's the UI:
Everything else seems to work -- if I leave it, then the CSV file is created as I suspect -- the Twython components seem to be working as expected.
Line 151 is where the streaming from Twitter is engaged when I click start:
self.stream.statuses.filter(track=self.search_term)
How can I move the streaming to a separate thread and then use the Stop button on the UI to tell Twython to complete capturing the stream and exit?
I need to be able to send the MyStreamer instance to another thread and then send it the .disconnect() signal to have it terminate capturing the stream.
Here's the full code:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import sys
import platform
import PySide
from PySide.QtGui import QApplication, QMainWindow, QPushButton, QCheckBox, QTextEdit
from time import sleep
from ui_tweetstream import Ui_MainWindow
from twython import Twython
from twython import TwythonStreamer
import csv
class MainWindow(QMainWindow, Ui_MainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.setupUi(self)
# Set up Variables
self.tweet_fav_count = True
self.tweet_geocoordinates = True
self.tweet_id = True
self.tweet_language = True
self.tweet_orig_tweet_id = True
self.tweet_orig_username = True
self.tweet_retweeted = True
self.tweet_sensitive = True
self.tweet_source_app = True
self.tweet_timestamp = True
self.tweet_user_name = True
self.search_term = "#bigdata"
self.tweets_to_get = 1000
# Bind the interface
self.check_tweet_fav_count.clicked.connect(self.setTweetFavCount)
self.check_tweet_geocoordinates.clicked.connect(self.setTweetGeocoordinates)
self.check_tweet_id.clicked.connect(self.setTweetID)
self.check_tweet_language.clicked.connect(self.setTweetLanguage)
self.check_tweet_orig_tweet_id.clicked.connect(self.setTweetOrigTweetID)
self.check_tweet_orig_username.clicked.connect(self.setTweetOrigUsername)
self.check_tweet_retweeted.clicked.connect(self.setTweetRetweeted)
self.check_tweet_sensitive.clicked.connect(self.setTweetSensitive)
self.check_tweet_source_app.clicked.connect(self.setTweetSourceApp)
self.check_tweet_timestamp.clicked.connect(self.setTweetTimestamp)
self.check_tweet_user_name.clicked.connect(self.setTweetUsername)
self.button_start.clicked.connect(self.streamStart)
self.button_stop.clicked.connect(self.streamStop)
# Set the initial states
self.button_stop.setEnabled(False)
APP_KEY = ''
APP_SECRET = ''
OAUTH_TOKEN = ''
OAUTH_TOKEN_SECRET = ''
self.t = Twython(APP_KEY, APP_SECRET, OAUTH_TOKEN, OAUTH_TOKEN_SECRET)
self.stream = MyStreamer(APP_KEY,APP_SECRET,OAUTH_TOKEN,OAUTH_TOKEN_SECRET)
self.stream.init_mainWindow(self)
def streamStop(self):
print "Stopping stream"
# Enable other controls here
self.button_stop.setEnabled(False)
self.button_start.setEnabled(True)
self.setControlStates(True)
self.stream.stopStream()
def setControlStates(self, state):
self.check_tweet_fav_count.setEnabled(state)
self.check_tweet_geocoordinates.setEnabled(state)
self.check_tweet_id.setEnabled(state)
self.check_tweet_language.setEnabled(state)
self.check_tweet_orig_tweet_id.setEnabled(state)
self.check_tweet_orig_username.setEnabled(state)
self.check_tweet_retweeted.setEnabled(state)
self.check_tweet_sensitive.setEnabled(state)
self.check_tweet_source_app.setEnabled(state)
self.check_tweet_timestamp.setEnabled(state)
self.check_tweet_user_name.setEnabled(state)
self.search_box.setEnabled(state)
self.num_tweets_box.setEnabled(state)
# Functions for determining what to track
def setTweetFavCount(self):
self.tweet_fav_count = not self.tweet_fav_count
print "tweet_fav_count:", self.tweet_fav_count
def setTweetGeocoordinates(self):
self.tweet_geocoordinates = not self.tweet_geocoordinates
print "tweet_geocoordinates:", self.tweet_geocoordinates
def setTweetID(self):
self.tweet_id = not self.tweet_id
print "tweet_id:", self.tweet_id
def setTweetLanguage(self):
self.tweet_language = not self.tweet_language
print "tweet_language:", self.tweet_language
def setTweetOrigTweetID(self):
self.tweet_orig_tweet_id = not self.tweet_orig_tweet_id
print "tweet_orig_tweet_id:", self.tweet_orig_tweet_id
def setTweetOrigUsername(self):
self.tweet_orig_username = not self.tweet_orig_tweet_id
print "tweet_orig_username:", self. tweet_orig_username
def setTweetRetweeted(self):
self.tweet_retweeted = not self.tweet_retweeted
print "tweet_retweeted:", self.tweet_retweeted
def setTweetSensitive(self):
self.tweet_sensitive = not self.tweet_sensitive
print "tweet_sensitive:", self.tweet_sensitive
def setTweetSourceApp(self):
self.tweet_source_app = not self.tweet_source_app
print "tweet_source_app:", self.tweet_source_app
def setTweetTimestamp(self):
self.tweet_timestamp = not self.tweet_timestamp
print "tweet_timestamp:", self.tweet_timestamp
def setTweetUsername(self):
self.tweet_user_name = not self.tweet_user_name
print "tweet_user_name:", self.tweet_user_name
# Functions for starting and stopping the stream
def streamStart(self):
print "Starting stream"
self.setControlStates(False)
# Disable other controls here
self.button_start.setEnabled(False)
self.button_stop.setEnabled(True)
# Hack to try to disable the UI
# sleep(0.25)
# Get the active search term
self.search_term = self.search_box.text()
# Get the number of tweets
self.tweets_to_get = int(self.num_tweets_box.text())
# Set the streamer
self.stream.set_start_criteria(self.tweets_to_get)
self.stream.statuses.filter(track=self.search_term)
class MyStreamer(TwythonStreamer):
def init_mainWindow(self, the_main_window):
self.main_window = the_main_window
self.stop = False
self.header_done = False
def set_start_criteria(self, numTweets):
self.maxTweets = numTweets
self.tweetCount = 0
print "Number of tweets to get:", self.maxTweets
def stopStream(self):
self.stop = True
def on_success(self, data):
if 'text' in data:
self.tweetCount += 1
print "tweetCount:", self.tweetCount
#tweet = data['text'].encode('utf-8')
theTweet = data
writer = TweetMonkey()
writer.assignMainWindow(self.main_window, self.header_done)
self.header_done = True
writer.process(theTweet)
# Want to disconnect after the first result?
if self.stop is True or self.tweetCount >= self.maxTweets:
self.disconnect()
def on_error(self, status_code, data):
print status_code, data
class TweetMonkey:
def assignMainWindow(self,the_main_window, is_header_done):
self.main_window = the_main_window
self.header_done = is_header_done
def clean(self,text):
text = text.replace("\n","; ")
text = text.replace('"', "'")
text = text.replace(','," ")
return text
def create_header(self):
header = []
tweets = open("tweets.csv", 'ab+')
wr = csv.writer(tweets, dialect='excel')
if self.main_window.tweet_id is True:
header.append("id")
if self.main_window.tweet_language is True:
header.append("lang")
if self.main_window.tweet_user_name is True:
header.append("user_name")
header.append("tweet")
if self.main_window.tweet_retweeted is True:
header.append("retweeted")
if self.main_window.tweet_fav_count is True:
header.append("favorite_count")
if self.main_window.tweet_source_app is True:
header.append("source")
if self.main_window.tweet_orig_tweet_id is True:
header.append("in_reply_to_status_id")
if self.main_window.tweet_orig_username is True:
header.append("in_reply_to_screen_name")
# header.append("in_reply_to_user_id")
if self.main_window.tweet_sensitive is True:
header.append("possibly_sensitive")
if self.main_window.tweet_geocoordinates is True:
header.append("geo")
if self.main_window.tweet_timestamp is True:
header.append("created_at")
wr.writerow(header)
tweets.close()
def process(self, tweet):
if not self.header_done:
self.create_header()
self.header_done = True
# Create the file or append to the existing
theOutput = []
tweets = open("tweets.csv", 'ab+')
wr = csv.writer(tweets, dialect='excel')
if self.main_window.tweet_id is True:
theOutput.append(tweet['id'])
if self.main_window.tweet_language is True:
theOutput.append(tweet['lang'].encode('utf-8'))
if self.main_window.tweet_user_name is True:
theOutput.append(tweet['user']['name'].encode('utf-8', 'replace'))
theOutput.append(self.clean(tweet['text']).encode('utf-8', 'replace'))
if self.main_window.tweet_retweeted is True:
theOutput.append(tweet['retweeted'])
if self.main_window.tweet_fav_count is True:
theOutput.append(tweet['favorite_count'])
if self.main_window.tweet_source_app is True:
theOutput.append(self.clean(tweet['source']).encode('utf-8', 'replace'))
if self.main_window.tweet_orig_tweet_id is True:
theOutput.append(tweet['in_reply_to_status_id'])
if self.main_window.tweet_orig_username is True:
theOutput.append(tweet['in_reply_to_screen_name'])
#theOutput.append(tweet['in_reply_to_user_id'])
if self.main_window.tweet_sensitive is True:
if tweet.get('possibly_sensitive'):
theOutput.append(tweet['possibly_sensitive'])
else:
theOutput.append("False")
if self.main_window.tweet_geocoordinates is True:
if tweet['geo'] is not None:
if tweet['geo']['type'] == 'Point':
lat = str(tweet['geo']['coordinates'][0]) + " "
lon = str(tweet['geo']['coordinates'][1])
theOutput.append(lat + lon)
else:
theOutput.append(tweet['geo'])
else:
theOutput.append(tweet['geo'])
if self.main_window.tweet_timestamp is True:
theOutput.append(tweet['created_at'])
wr.writerow(theOutput)
tweets.close()
if __name__ == '__main__':
app = QApplication(sys.argv)
frame = MainWindow()
frame.show()
app.exec_()

I know this is an old post but I ran into a similar problem in a simple app I recently wrote, my solution was to use threading.
I used the worker from:
https://pymotw.com/2/threading/
and the method described in:
http://aadrake.com/using-twitter-as-a-stream-processing-source.html
Basically running the Twython stream as a separate thread feeding text to a queue then I run the rest of the program in a separate loop reading from the queue.

Set attribute on a python thread from traits

I am new to python and I am implementing a simple serial adquisition in a thread.
I can adquire the data using a class by
class CaptureAngles(threading.Thread, port)
def __init__(self):
threading.Thread.__init__(self)
self.port_name = port
...
def run():
self.connect(self.port_name)
...
However, to better integrate with a graphical interface using the traits library I wrote the code as the following, which is no longer working. I am not able to define the attribute of a thread that is started from traits, what am I doing wrong?
This is the error reported
AttributeError: 'CaptureAngles' object has no attribute 'port_name'
And this the full code:
from threading import Thread
from time import sleep
from enthought.traits.api import *
from enthought.traits.ui.api import View, Item, ButtonEditor
from Queue import Queue
class TextDisplay(HasTraits):
string = String()
view= View( Item('string',show_label=False, springy=True, style='custom' ))
class CaptureAngles(Thread):
self.port_name = String('COM5')
def connect(self, port_name):
self.port = serial.Serial(
port = port_name,
baudrate = 9600,
)
self.display.string='Opening Serial Port...' + self.display.string
self.port.close()
self.port.open()
def run(self):
self.connect(self.port_name)
self.display.string = 'Arduino started\n' + self.display.string
self.port.flushInput()
self.port.flushOutput()
self.port.readline() # Discard first package (can be corrupt)
while not self.wants_abort:
rcv = self.port.readline() # Read the data and split into words
angle = int(rcv)
self.display.string = '%d angle captured\n' % n_img \
+ self.display.string
self.close()
def close(self):
self.port.close()
self.display.string='...Serial Port Closed!' + self.display.string
class Arduino(HasTraits):
start_stop_capture = Button()
display = Instance(TextDisplay)
capture_angles = Instance(CaptureAngles)
capture_angles.port_name = 'COM5'
view = View(Item('start_stop_capture', show_label=False ))
def _start_stop_capture_fired(self):
if self.capture_angles and self.capture_angles.isAlive():
self.capture_angles.wants_abort = True
else:
self.capture_angles = CaptureAngles()
self.capture_angles.wants_abort = False
self.capture_angles.display = self.display
self.capture_angles.start()
class MainWindow(HasTraits):
display = Instance(TextDisplay, ())
arduino = Instance(Arduino)
def _arduino_default(self):
return Arduino(display=self.display)
view = View('arduino','display', style="custom", resizable=True)
if __name__ == '__main__':
MainWindow().configure_traits()

Ok, I got it: I was adding the attribute port_name before creating the instance.
class Arduino(HasTraits):
start_stop_capture = Button()
display = Instance(TextDisplay)
capture_angles = Instance(CaptureAngles)
capture_angles.port_name = 'COM5' # <-- wrong: the object is not created yet
...
instead of:
def _start_stop_capture_fired(self):
if self.capture_angles and self.capture_angles.isAlive():
self.capture_angles.wants_abort = True
else:
self.capture_angles = CaptureAngles()
self.capture_angles.port_name = 'COM5' # <-- correct
...

convert winsound to a linux platform?

On a chat script I was working on a while back, I used the winsound python library to play a 'ding' sound (ding.wav) when a new message was received. Now I am wondering how I can make this work for linux, only with a .ogg audio file. The code is below:
import sys
import util
import thread
import socket
import winsound
class ClientSocket():
rbufsize = -1
wbufsize = 0
def __init__(self, address, nickname=''):
if type(address) == type(()) and type(address[0]) == type('') and type(address[1]) == type(1):
pass
else:
print ('Address is of incorrect type. \n' +
'Must be (serverHost (str), serverPort (int)).')
sys.exit(1)
if nickname:
self.changeNick(nickname)
else:
self.changeNick(raw_input('Nickname: '))
self.prompt_on = False
self.address = address
def connect(self):
self.connection=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
self.connection.connect(self.address)
self.rfile = self.connection.makefile('rb', self.rbufsize)
self.wfile = self.connection.makefile('wb', self.wbufsize)
self.wfile.write('/nick ' + self.nickname + '\n')
def serve_forever(self):
self.connect()
thread.start_new_thread(self.acceptinput,())
line = ""
while line not in ('/exit','/quit', '/q'):
self.prompt_on = True
line = raw_input(self.prompt)
self.prompt_on = False
if line[:2] == '/n' or line[:5] == '/nick':
self.changeNick(line.split(' ', 1)[1].strip())
self.wfile.write(line + '\n')
self.close()
self.connection.shutdown(socket.SHUT_RDWR)
self.connection.close()
def changeNick(self, newNick):
self.nickname = newNick
self.prompt = self.nickname+': '
self.backspace = '\b' * len(self.prompt)
def acceptinput(self):
while 1:
data = self.rfile.readline().strip()
if data:
self.writedata(data)
if 'Nickname successfully changed to' in data:
self.changeNick(data.split('"')[1])
def writedata(self, data):
if self.prompt_on:
output = data if len(data) >= len(self.prompt) else data + ' ' * (len(self.prompt) - len(data))
winsound.PlaySound("ding.wav", winsound.SND_FILENAME)
sys.stdout.write(self.backspace + output + '\n' + self.prompt)
sys.stdout.flush()
else:
print data
def close(self):
if not self.wfile.closed:
self.wfile.flush()
self.wfile.close()
self.rfile.close()
def main():
serverHost = raw_input('Server IP/Hostname: ')
if not serverHost:
serverHost = util.getIP()
else:
serverHost = socket.gethostbyname(serverHost)
serverPort = input('Server Port: ')
address = (serverHost, serverPort)
client = ClientSocket(address)
print 'Connecting to server on %s:%s' % (serverHost, serverPort)
client.serve_forever()
if __name__ == '__main__':
main()
If someone could help me convert this to play a .ogg file instead, it would be awesome:)
Thanks, Sean.

In the end, I ended up using the pygame library:
import pygame
pygame.init()
pygame.mixer.music.load("ding.ogg")
pygame.mixer.music.play()

PyQt QTcpServer: How to return data to multiple clients?

I am looking to create a QTcpServer using PyQt that can simultaneously return data to 2 or more clients. I assume that this will require threading.
Using the threadedfortuneserver.py example as a test case (included with PyQt4, on my system it is found in /usr/share/doc/python-qt4-doc/examples/network), I want to connect multiple clients and each time one of the clients asks for a fortune, the other clients also get updated with a message like "Client X just received the fortune 'blah blah blah'".
I understand how the fortuneserver/client program works, but it seems that the client connections are immediately terminated after the fortune is sent back to the client. My specific questions are:
Is it possible to keep all of the connections open so that every
time one of the clients requests a fortune, the other clients can be
updated?
If so, what is the best way to keep track of and loop over the connected clients?
This is a serious stumbling block for me because I want to develop an app where several clients can interact, and each client can be updated about the actions of the other clients.
Thanks in advance for your help, let me know if there is any other information I can provide.
I found this thread but there wasn't enough specific information to make use of. Other discussions have been for the Python socket package, but it is my understanding that when using PyQt, the server should be a QTcpServer so everything plays nice.
*** EDIT ***
Here are the beginning stages of my solution. I have created a basic server and client. The server just sends back what the client entered into a Line Edit box.
I am basing this on the "buildingservices" example from Chapter 18 of Rapid GUI Programming with Python and Qt.
The major change I made is that now the threads keep running indefinitely and their sockets stay open, listening for data being sent by the client.
It handles multiple clients fine. It is certainly ugly, but I think it is a good starting point.
What I would like is to be able to notify each client whenever one client enters text (like a typical chat program, say).
Also, to give you an idea of who you are dealing with, I am NOT a professional programmer. I am a physicist with many years of undisciplined scripting and fiddling around under my belt. But I would like to try to develop basic server/client programs that can pass data around.
Thanks for any help or suggestions!
SERVER:
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyQt4.QtNetwork import *
PORT = 9999
SIZEOF_UINT16 = 2
class Thread(QThread):
#lock = QReadWriteLock()
def __init__(self, socketId, parent):
super(Thread, self).__init__(parent)
self.socketId = socketId
def run(self):
self.socket = QTcpSocket()
if not self.socket.setSocketDescriptor(self.socketId):
self.emit(SIGNAL("error(int)"), socket.error())
return
while self.socket.state() == QAbstractSocket.ConnectedState:
nextBlockSize = 0
stream = QDataStream(self.socket)
stream.setVersion(QDataStream.Qt_4_2)
if (self.socket.waitForReadyRead(-1) and
self.socket.bytesAvailable() >= SIZEOF_UINT16):
nextBlockSize = stream.readUInt16()
else:
self.sendError("Cannot read client request")
return
if self.socket.bytesAvailable() < nextBlockSize:
if (not self.socket.waitForReadyRead(-1) or
self.socket.bytesAvailable() < nextBlockSize):
self.sendError("Cannot read client data")
return
textFromClient = stream.readQString()
textToClient = "You wrote: \"{}\"".format(textFromClient)
self.sendReply(textToClient)
def sendError(self, msg):
reply = QByteArray()
stream = QDataStream(reply, QIODevice.WriteOnly)
stream.setVersion(QDataStream.Qt_4_2)
stream.writeUInt16(0)
stream.writeQString("ERROR")
stream.writeQString(msg)
stream.device().seek(0)
stream.writeUInt16(reply.size() - SIZEOF_UINT16)
self.socket.write(reply)
def sendReply(self, text):
reply = QByteArray()
stream = QDataStream(reply, QIODevice.WriteOnly)
stream.setVersion(QDataStream.Qt_4_2)
stream.writeUInt16(0)
stream.writeQString(text)
stream.device().seek(0)
stream.writeUInt16(reply.size() - SIZEOF_UINT16)
self.socket.write(reply)
class TcpServer(QTcpServer):
def __init__(self, parent=None):
super(TcpServer, self).__init__(parent)
def incomingConnection(self, socketId):
self.thread = Thread(socketId, self)
self.thread.start()
class ServerDlg(QPushButton):
def __init__(self, parent=None):
super(ServerDlg, self).__init__(
"&Close Server", parent)
self.setWindowFlags(Qt.WindowStaysOnTopHint)
self.tcpServer = TcpServer(self)
if not self.tcpServer.listen(QHostAddress("0.0.0.0"), PORT):
QMessageBox.critical(self, "Threaded Server",
"Failed to start server: {}".format(
self.tcpServer.errorString()))
self.close()
return
self.connect(self, SIGNAL("clicked()"), self.close)
font = self.font()
font.setPointSize(24)
self.setFont(font)
self.setWindowTitle("Threaded Server")
app = QApplication(sys.argv)
form = ServerDlg()
form.show()
form.move(0, 0)
app.exec_()
CLIENT:
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyQt4.QtNetwork import *
PORT = 9999
SIZEOF_UINT16 = 2
class Form(QDialog):
def __init__(self, parent=None):
super(Form, self).__init__(parent)
# Ititialize socket
self.socket = QTcpSocket()
# Initialize data IO variables
self.nextBlockSize = 0
self.request = None
# Create widgets/layout
self.browser = QTextBrowser()
self.lineedit = QLineEdit("Texty bits")
self.lineedit.selectAll()
self.connectButton = QPushButton("Connect")
self.connectButton.setDefault(False)
self.connectButton.setEnabled(True)
layout = QVBoxLayout()
layout.addWidget(self.browser)
layout.addWidget(self.lineedit)
layout.addWidget(self.connectButton)
self.setLayout(layout)
self.lineedit.setFocus()
# Signals and slots for line edit and connect button
self.lineedit.returnPressed.connect(self.sendToServer)
self.connectButton.released.connect(self.connectToServer)
self.setWindowTitle("Client")
# Signals and slots for networking
self.socket.readyRead.connect(self.readFromServer)
self.socket.disconnected.connect(self.serverHasStopped)
self.connect(self.socket,
SIGNAL("error(QAbstractSocket::SocketError)"),
self.serverHasError)
# Update GUI
def updateUi(self, text):
self.browser.append(text)
# Create connection to server
def connectToServer(self):
self.connectButton.setEnabled(False)
print("Connecting to server")
self.socket.connectToHost("localhost", PORT)
# Send data to server
def sendToServer(self):
self.request = QByteArray()
stream = QDataStream(self.request, QIODevice.WriteOnly)
stream.setVersion(QDataStream.Qt_4_2)
stream.writeUInt16(0)
stream.writeQString(self.lineedit.text())
stream.device().seek(0)
stream.writeUInt16(self.request.size() - SIZEOF_UINT16)
self.socket.write(self.request)
self.nextBlockSize = 0
self.request = None
self.lineedit.setText("")
# Read data from server and update Text Browser
def readFromServer(self):
stream = QDataStream(self.socket)
stream.setVersion(QDataStream.Qt_4_2)
while True:
if self.nextBlockSize == 0:
if self.socket.bytesAvailable() < SIZEOF_UINT16:
break
self.nextBlockSize = stream.readUInt16()
if self.socket.bytesAvailable() < self.nextBlockSize:
break
textFromServer = stream.readQString()
self.updateUi(textFromServer)
self.nextBlockSize = 0
def serverHasStopped(self):
self.socket.close()
def serverHasError(self):
self.updateUi("Error: {}".format(
self.socket.errorString()))
self.socket.close()
app = QApplication(sys.argv)
form = Form()
form.show()
app.exec_()

As was probably exasperatingly obvious to most of you, I didn't fully understand how to deal with threads! Not to worry, I have discovered a way to design a server that can send data to multiple clients with nary a secondary thread to be found.
Quite simple, really, but I'm not the quickest of cats at the best of times.
SERVER:
#!/usr/bin/env python3
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyQt4.QtNetwork import *
PORT = 9999
SIZEOF_UINT32 = 4
class ServerDlg(QPushButton):
def __init__(self, parent=None):
super(ServerDlg, self).__init__(
"&Close Server", parent)
self.setWindowFlags(Qt.WindowStaysOnTopHint)
self.tcpServer = QTcpServer(self)
self.tcpServer.listen(QHostAddress("0.0.0.0"), PORT)
self.connect(self.tcpServer, SIGNAL("newConnection()"),
self.addConnection)
self.connections = []
self.connect(self, SIGNAL("clicked()"), self.close)
font = self.font()
font.setPointSize(24)
self.setFont(font)
self.setWindowTitle("Server")
def addConnection(self):
clientConnection = self.tcpServer.nextPendingConnection()
clientConnection.nextBlockSize = 0
self.connections.append(clientConnection)
self.connect(clientConnection, SIGNAL("readyRead()"),
self.receiveMessage)
self.connect(clientConnection, SIGNAL("disconnected()"),
self.removeConnection)
self.connect(clientConnection, SIGNAL("error()"),
self.socketError)
def receiveMessage(self):
for s in self.connections:
if s.bytesAvailable() > 0:
stream = QDataStream(s)
stream.setVersion(QDataStream.Qt_4_2)
if s.nextBlockSize == 0:
if s.bytesAvailable() < SIZEOF_UINT32:
return
s.nextBlockSize = stream.readUInt32()
if s.bytesAvailable() < s.nextBlockSize:
return
textFromClient = stream.readQString()
s.nextBlockSize = 0
self.sendMessage(textFromClient,
s.socketDescriptor())
s.nextBlockSize = 0
def sendMessage(self, text, socketId):
for s in self.connections:
if s.socketDescriptor() == socketId:
message = "You> {}".format(text)
else:
message = "{}> {}".format(socketId, text)
reply = QByteArray()
stream = QDataStream(reply, QIODevice.WriteOnly)
stream.setVersion(QDataStream.Qt_4_2)
stream.writeUInt32(0)
stream.writeQString(message)
stream.device().seek(0)
stream.writeUInt32(reply.size() - SIZEOF_UINT32)
s.write(reply)
def removeConnection(self):
pass
def socketError(self):
pass
app = QApplication(sys.argv)
form = ServerDlg()
form.show()
form.move(0, 0)
app.exec_()
CLIENT
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyQt4.QtNetwork import *
PORTS = (9998, 9999)
PORT = 9999
SIZEOF_UINT32 = 4
class Form(QDialog):
def __init__(self, parent=None):
super(Form, self).__init__(parent)
# Ititialize socket
self.socket = QTcpSocket()
# Initialize data IO variables
self.nextBlockSize = 0
self.request = None
# Create widgets/layout
self.browser = QTextBrowser()
self.lineedit = QLineEdit("Enter text here, dummy")
self.lineedit.selectAll()
self.connectButton = QPushButton("Connect")
self.connectButton.setEnabled(True)
layout = QVBoxLayout()
layout.addWidget(self.browser)
layout.addWidget(self.lineedit)
layout.addWidget(self.connectButton)
self.setLayout(layout)
self.lineedit.setFocus()
# Signals and slots for line edit and connect button
self.lineedit.returnPressed.connect(self.issueRequest)
self.connectButton.clicked.connect(self.connectToServer)
self.setWindowTitle("Client")
# Signals and slots for networking
self.socket.readyRead.connect(self.readFromServer)
self.socket.disconnected.connect(self.serverHasStopped)
self.connect(self.socket,
SIGNAL("error(QAbstractSocket::SocketError)"),
self.serverHasError)
# Update GUI
def updateUi(self, text):
self.browser.append(text)
# Create connection to server
def connectToServer(self):
self.connectButton.setEnabled(False)
self.socket.connectToHost("localhost", PORT)
def issueRequest(self):
self.request = QByteArray()
stream = QDataStream(self.request, QIODevice.WriteOnly)
stream.setVersion(QDataStream.Qt_4_2)
stream.writeUInt32(0)
stream.writeQString(self.lineedit.text())
stream.device().seek(0)
stream.writeUInt32(self.request.size() - SIZEOF_UINT32)
self.socket.write(self.request)
self.nextBlockSize = 0
self.request = None
self.lineedit.setText("")
def readFromServer(self):
stream = QDataStream(self.socket)
stream.setVersion(QDataStream.Qt_4_2)
while True:
if self.nextBlockSize == 0:
if self.socket.bytesAvailable() < SIZEOF_UINT32:
break
self.nextBlockSize = stream.readUInt32()
if self.socket.bytesAvailable() < self.nextBlockSize:
break
textFromServer = stream.readQString()
self.updateUi(textFromServer)
self.nextBlockSize = 0
def serverHasStopped(self):
self.socket.close()
self.connectButton.setEnabled(True)
def serverHasError(self):
self.updateUi("Error: {}".format(
self.socket.errorString()))
self.socket.close()
self.connectButton.setEnabled(True)
app = QApplication(sys.argv)
form = Form()
form.show()
app.exec_()
To summarize, each client connection opens a socket, and the socket is appended to a list of all client sockets. Then, when one of the clients sends text, the server loops over the client sockets, finds the one that has bytesAvailable, reads it in, and then sends the message to the other clients.
I would be curious to hear what other people may think of this approach. Pitfalls, issues, etc.
Thanks!

Here is the shareable code for PyQt5!
QTcpServer ==================
import sys
from PyQt5.QtCore import Qt, QDataStream, QByteArray, QIODevice, pyqtSignal
from PyQt5.QtWidgets import QApplication, QPushButton
from PyQt5.QtNetwork import QTcpServer, QHostAddress
PORT = 9999
SIZEOF_UINT32 = 4
class ServerDlg(QPushButton):
def __init__(self, parent=None):
super(ServerDlg, self).__init__(
"&Close Server", parent)
self.setWindowFlags(Qt.WindowStaysOnTopHint)
self.tcpServer = QTcpServer(self)
self.tcpServer.listen(QHostAddress("127.0.0.1"), PORT)
self.tcpServer.newConnection.connect(self.addConnection)
self.connections = []
self.clicked.connect(self.close)
font = self.font()
font.setPointSize(24)
self.setFont(font)
self.setWindowTitle("Server")
def addConnection(self):
clientConnection = self.tcpServer.nextPendingConnection()
clientConnection.nextBlockSize = 0
self.connections.append(clientConnection)
clientConnection.readyRead.connect(self.receiveMessage)
clientConnection.disconnected.connect(self.removeConnection)
clientConnection.errorOccurred.connect(self.socketError)
def receiveMessage(self):
for s in self.connections:
if s.bytesAvailable() > 0:
stream = QDataStream(s)
stream.setVersion(QDataStream.Qt_4_2)
if s.nextBlockSize == 0:
if s.bytesAvailable() < SIZEOF_UINT32:
return
s.nextBlockSize = stream.readUInt32()
if s.bytesAvailable() < s.nextBlockSize:
return
textFromClient = stream.readQString()
s.nextBlockSize = 0
self.sendMessage(textFromClient,
s.socketDescriptor())
s.nextBlockSize = 0
print('Connections ', self.connections)
def sendMessage(self, text, socketId):
print('Text ', text)
for s in self.connections:
if s.socketDescriptor() == socketId:
message = "You> {}".format(text)
else:
message = "{}> {}".format(socketId, text)
reply = QByteArray()
stream = QDataStream(reply, QIODevice.WriteOnly)
stream.setVersion(QDataStream.Qt_4_2)
stream.writeUInt32(0)
stream.writeQString(message)
stream.device().seek(0)
stream.writeUInt32(reply.size() - SIZEOF_UINT32)
s.write(reply)
def removeConnection(self):
pass
def socketError(self):
pass
app = QApplication(sys.argv)
form = ServerDlg()
form.show()
form.move(0, 0)
app.exec_()