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PyQt5 Gui Thread to worker Thread signal/Slot

I am trying to make a simple communication between a worker thread, in this case it is called WorkToDo via the PyQt5 Signals and Slots mechanism. I can reliably send data from the Worker to the Gui thread via this mechanism, but I cannot do the same to the gui thread. From my research I have found that this is due to the fact that I have overridden the run function with my own logic. My question, is there any way to manually handle the execution of signals in the worker thread? Is there a better way to accomplish this?
EDIT:
I am actually not overriding run as I do not see run listed in the documentation for QObject. I am mistaken as this is a default function of a QThread object. This is more perplexing to me. Unless I am just further misunderstanding this.
import sys
import time
import qdarkstyle
from PyQt5.QtWidgets import (
QWidget, QLineEdit, QMessageBox, QPushButton, QVBoxLayout, QHBoxLayout, QTabWidget,
QComboBox, QProgressBar, QApplication, QLabel, QGroupBox, QFileDialog, QTextEdit,
QStyleFactory, QFormLayout
)
from PyQt5 import (Qt, QtCore)
from PyQt5.QtCore import *
class Command:
def __init__(self, **kwargs):
self.cmd = kwargs.get('cmd', None)
self.args = kwargs.get('args')
class CommandSignals(QObject):
command = pyqtSignal(Command)
class WorkToDo(QObject):
def __init__(self):
super().__init__()
self.counter = 0
self.signals = CommandSignals()
#QtCore.pyqtSlot(Command)
def process_command(self, command):
"""
#brief process update from gui thread
#param self self
#param command command
#return none
"""
print(f'Update from GUI: {command.__dict__}')
if command.cmd == 'add_to_counter':
self.counter = self.counter + command.args.get('addition', 0)
#pyqtSlot()
def run(self):
"""
#brief actual thread function to run,
started via thread.started signal (why its decorated with a pyqtSlot)
#param self obj ref
#return none
"""
while True:
QThread.sleep(1)
# emit text change signal to main gui thread
cmd = Command(
cmd = 'update_text',
args = {
'text': f'Hello update {self.counter}'
}
)
print(f'Update from worker: {cmd.__dict__}')
self.signals.command.emit(cmd)
self.counter += 1
class Gui(QWidget):
def __init__(self):
super().__init__()
""" make gui elements """
layout = QFormLayout()
self.text_line = QLineEdit()
self.add_button = QPushButton('Add 10 To Counter')
layout.addRow(self.text_line)
layout.addRow(self.add_button)
self.add_button.clicked.connect(self.issue_button_update)
self.signals = CommandSignals()
self.MakeThreadWorker()
""" finalize gui """
self.setLayout(layout)
self.setWindowTitle('Sync Thread Command/Response test')
self.show()
def MakeThreadWorker(self):
self.worker_thread = QThread()
self.worker = WorkToDo()
""" incoming gui update command, works """
self.worker.signals.command.connect(self.process_command)
""" outgoing update to worker thread, does not work """
self.signals.command.connect(self.worker.process_command)
""" signal to start the thread function, works """
self.worker_thread.started.connect(self.worker.run)
self.worker_thread.start()
self.worker.moveToThread(self.worker_thread)
#pyqtSlot(Command)
def process_command(self, command):
"""
#brief process update from work thread
#param self self
#param command command object
#return none
"""
if command.cmd == 'update_text':
text_update = command.args.get('text', '')
self.text_line.setText(text_update)
def issue_button_update(self):
cmd = Command(
cmd = 'add_to_counter',
args = {
'addition': 10
}
)
print('Button Clicked!')
self.signals.command.emit(cmd)
if __name__ == '__main__':
APPLICATION = QApplication([])
APPLICATION.setStyleSheet(qdarkstyle.load_stylesheet_pyqt5())
gui = Gui()
sys.exit(APPLICATION.exec_())

The problem is that with True while you are blocking the event loop of the secondary thread preventing the signals from being received, if you want to do a periodic task then use a QTimer.
import sys
import time
import qdarkstyle
from PyQt5.QtCore import pyqtSignal, pyqtSlot, QObject, QThread, QTimer
from PyQt5.QtWidgets import QApplication, QFormLayout, QLineEdit, QPushButton, QWidget
class Command:
def __init__(self, **kwargs):
self.cmd = kwargs.get("cmd", None)
self.args = kwargs.get("args")
class CommandSignals(QObject):
command = pyqtSignal(Command)
class WorkToDo(QObject):
def __init__(self):
super().__init__()
self.counter = 0
self.signals = CommandSignals()
self.timer = QTimer(self, timeout=self.run, interval=1000)
#pyqtSlot()
def start(self):
self.timer.start()
#pyqtSlot()
def stop(self):
self.timer.stop()
#pyqtSlot(Command)
def process_command(self, command):
"""
#brief process update from gui thread
#param self self
#param command command
#return none
"""
print(f"Update from GUI: {command.__dict__}")
if command.cmd == "add_to_counter":
self.counter = self.counter + command.args.get("addition", 0)
#pyqtSlot()
def run(self):
print(self.thread(), self.timer.thread())
cmd = Command(cmd="update_text", args={"text": f"Hello update {self.counter}"})
print(f"Update from worker: {cmd.__dict__}")
self.signals.command.emit(cmd)
self.counter += 1
class Gui(QWidget):
def __init__(self):
super().__init__()
""" make gui elements """
layout = QFormLayout()
self.text_line = QLineEdit()
self.add_button = QPushButton("Add 10 To Counter")
layout.addRow(self.text_line)
layout.addRow(self.add_button)
self.add_button.clicked.connect(self.issue_button_update)
self.signals = CommandSignals()
self.MakeThreadWorker()
""" finalize gui """
self.setLayout(layout)
self.setWindowTitle("Sync Thread Command/Response test")
self.show()
def MakeThreadWorker(self):
self.worker_thread = QThread()
self.worker = WorkToDo()
""" incoming gui update command, works """
self.worker.signals.command.connect(self.process_command)
""" outgoing update to worker thread, does not work """
self.signals.command.connect(self.worker.process_command)
""" signal to start the thread function, works """
self.worker_thread.started.connect(self.worker.start)
self.worker_thread.start()
self.worker.moveToThread(self.worker_thread)
#pyqtSlot(Command)
def process_command(self, command):
"""
#brief process update from work thread
#param self self
#param command command object
#return none
"""
if command.cmd == "update_text":
text_update = command.args.get("text", "")
self.text_line.setText(text_update)
def issue_button_update(self):
cmd = Command(cmd="add_to_counter", args={"addition": 10})
print("Button Clicked!")
self.signals.command.emit(cmd)
if __name__ == "__main__":
APPLICATION = QApplication([])
APPLICATION.setStyleSheet(qdarkstyle.load_stylesheet_pyqt5())
gui = Gui()
sys.exit(APPLICATION.exec_())

PyQt5 QThread not working, gui still freezing

I have this code (if you have pyqt5, you should be able to run it yourself):
import sys
import time
from PyQt5.QtWidgets import QApplication, QPushButton, QVBoxLayout, QWidget
from PyQt5.QtCore import QObject, QThread, pyqtSignal, pyqtSlot
class Worker(QObject):
def __init__(self):
super().__init__()
self.thread = None
class Tab(QObject):
def __init__(self, _main):
super().__init__()
self._main = _main
class WorkerOne(Worker):
finished = pyqtSignal()
def __init__(self):
super().__init__()
#pyqtSlot(str)
def print_name(self, name):
for _ in range(100):
print("Hello there, {0}!".format(name))
time.sleep(1)
self.finished.emit()
self.thread.quit()
class SomeTabController(Tab):
def __init__(self, _main):
super().__init__(_main)
self.threads = {}
self._main.button_start_thread.clicked.connect(self.start_thread)
# Workers
self.worker1 = WorkerOne()
#self.worker2 = WorkerTwo()
#self.worker3 = WorkerThree()
#self.worker4 = WorkerFour()
def _threaded_call(self, worker, fn, *args, signals=None, slots=None):
thread = QThread()
thread.setObjectName('thread_' + worker.__class__.__name__)
# store because garbage collection
self.threads[worker] = thread
# give worker thread so it can be quit()
worker.thread = thread
# objects stay on threads after thread.quit()
# need to move back to main thread to recycle the same Worker.
# Error is thrown about Worker having thread (0x0) if you don't do this
worker.moveToThread(QThread.currentThread())
# move to newly created thread
worker.moveToThread(thread)
# Can now apply cross-thread signals/slots
#worker.signals.connect(self.slots)
if signals:
for signal, slot in signals.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
#self.signals.connect(worker.slots)
if slots:
for slot, signal in slots.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
thread.started.connect(lambda: fn(*args)) # fn needs to be slot
thread.start()
#pyqtSlot()
def _receive_signal(self):
print("Signal received.")
#pyqtSlot(bool)
def start_thread(self):
name = "Bob"
signals = {self.worker1.finished: self._receive_signal}
self._threaded_call(self.worker1, self.worker1.print_name, name,
signals=signals)
class MainWindow(QWidget):
def __init__(self):
super().__init__()
self.setWindowTitle("Thread Example")
form_layout = QVBoxLayout()
self.setLayout(form_layout)
self.resize(400, 400)
self.button_start_thread = QPushButton()
self.button_start_thread.setText("Start thread.")
form_layout.addWidget(self.button_start_thread)
self.controller = SomeTabController(self)
if __name__ == '__main__':
app = QApplication(sys.argv)
_main = MainWindow()
_main.show()
sys.exit(app.exec_())
However WorkerOne still blocks my GUI thread and the window is non-responsive when WorkerOne.print_name is running.
I have been researching a lot about QThreads recently and I am not sure why this isn't working based on the research I've done.
What gives?

The problem is caused by the connection with the lambda method since this lambda is not part of the Worker so it does not run on the new thread. The solution is to use functools.partial:
from functools import partial
...
thread.started.connect(partial(fn, *args))
Complete Code:
import sys
import time
from functools import partial
from PyQt5.QtWidgets import QApplication, QPushButton, QVBoxLayout, QWidget
from PyQt5.QtCore import QObject, QThread, pyqtSignal, pyqtSlot
class Worker(QObject):
def __init__(self):
super().__init__()
self.thread = None
class Tab(QObject):
def __init__(self, _main):
super().__init__()
self._main = _main
class WorkerOne(Worker):
finished = pyqtSignal()
def __init__(self):
super().__init__()
#pyqtSlot(str)
def print_name(self, name):
for _ in range(100):
print("Hello there, {0}!".format(name))
time.sleep(1)
self.finished.emit()
self.thread.quit()
class SomeTabController(Tab):
def __init__(self, _main):
super().__init__(_main)
self.threads = {}
self._main.button_start_thread.clicked.connect(self.start_thread)
# Workers
self.worker1 = WorkerOne()
#self.worker2 = WorkerTwo()
#self.worker3 = WorkerThree()
#self.worker4 = WorkerFour()
def _threaded_call(self, worker, fn, *args, signals=None, slots=None):
thread = QThread()
thread.setObjectName('thread_' + worker.__class__.__name__)
# store because garbage collection
self.threads[worker] = thread
# give worker thread so it can be quit()
worker.thread = thread
# objects stay on threads after thread.quit()
# need to move back to main thread to recycle the same Worker.
# Error is thrown about Worker having thread (0x0) if you don't do this
worker.moveToThread(QThread.currentThread())
# move to newly created thread
worker.moveToThread(thread)
# Can now apply cross-thread signals/slots
#worker.signals.connect(self.slots)
if signals:
for signal, slot in signals.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
#self.signals.connect(worker.slots)
if slots:
for slot, signal in slots.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
thread.started.connect(partial(fn, *args)) # fn needs to be slot
thread.start()
#pyqtSlot()
def _receive_signal(self):
print("Signal received.")
#pyqtSlot(bool)
def start_thread(self):
name = "Bob"
signals = {self.worker1.finished: self._receive_signal}
self._threaded_call(self.worker1, self.worker1.print_name, name,
signals=signals)
class MainWindow(QWidget):
def __init__(self):
super().__init__()
self.setWindowTitle("Thread Example")
form_layout = QVBoxLayout()
self.setLayout(form_layout)
self.resize(400, 400)
self.button_start_thread = QPushButton()
self.button_start_thread.setText("Start thread.")
form_layout.addWidget(self.button_start_thread)
self.controller = SomeTabController(self)
if __name__ == '__main__':
app = QApplication(sys.argv)
_main = MainWindow()
_main.show()
sys.exit(app.exec_())

To avoid blocking the gui for a slideshow function showing images i run the following
simple code.
A background Thread Class to wait one second, then signal to the gui waiting is finished.
class Waiter(QThread):
result = pyqtSignal(object)
def __init__(self):
QtCore.QThread.__init__(self)
def run(self):
while self.isRunning:
self.sleep(1)
self.result.emit("waited for 1s")
Then in main window connect the slideshow start and stop button to start and stop methods of main app and connect the nextImage function to the signal the Waiter Thread emits.
self.actionstopSlideShow.triggered.connect(self.stopSlideShow)
self.actionslideShowStart.triggered.connect(self.startSlideShow)
self.waitthread = Waiter()
self.waitthread.result.connect(self.nextImage)
Then two methods of main app allow to start and stop the time ticker
def startSlideShow(self):
"""Start background thread that waits one second,
on wait result trigger next image
use thread otherwise gui freezes and stop button cannot be pressed
"""
self.waitthread.start()
def stopSlideShow(self):
self.waitthread.terminate()
self.waitthread.wait()
Up to now i have no problems subclassing from QThread in pyqt5, gui changes are all handled inside the main (gui) thread.

How to send signal from inside of imported function on pyqt5?

I have one Worker Thread on my program that returns a number every second, forever, until the stop signal is emmited on the Main Window. I want it to emit a signal everytime it changes a value, so I can update the Main Window with the returned value. I tried simply emmiting a signal in the function itself, but doesn't work.
Worker:
from test import save_data
class Worker(QObject):
finished = pyqtSignal() # give worker class a finished signal
def __init__(self, parent=None):
QObject.__init__(self, parent=parent)
def do_work(self):
save_data.main()
self.finished.emit() # emit the finished signal when the loop is done
def stop(self):
save_data.run = False # set the run condition to false on stop
test.py:
import time
from Pyqt5.QtCore import pyqtSignal
run = True
value = pyqtSignal(int)
def main():
x = 1
while run:
print(x)
x += 1
time.sleep(1)
#value.emit(x)

Final code:
from PyQt5.QtCore import QThread, QObject, pyqtSignal, pyqtSlot, Qt, QTimer
import time
class Main(QObject):
divisible_by_4 = pyqtSignal()
def __init__(self, parent=None):
QObject.__init__(self, parent=parent)
self.run = True
def main(self):
x = 1
while self.run:
print(x)
x += 1
if x%4 == 0:
self.divisible_by_4.emit()
time.sleep(1)
def stop(self):
self.run = False

PyQt: moveToThread does not work when using partial() for slot

I am building a small GUI application which runs a producer (worker) and the GUI consumes the output on demand and plots it (using pyqtgraph).
Since the producer is a blocking function (takes a while to run), I (supposedly) moved it to its own thread.
When calling QThread.currentThreadId() from the producer it outputs the same number as the main GUI thread. So, the worker is executed first, and then all the plotting function calls are executed (because they are being queued on the same thread's event queue). How can I fix this?
Example run with partial:
gui thread id 140665453623104
worker thread id: 140665453623104
Here is my full code:
from PyQt4 import QtCore, QtGui
from PyQt4.QtCore import pyqtSignal
import pyqtgraph as pg
import numpy as np
from functools import partial
from Queue import Queue
import math
import sys
import time
class Worker(QtCore.QObject):
termino = pyqtSignal()
def __init__(self, q=None, parent=None):
super(Worker, self).__init__(parent)
self.q = q
def run(self, m=30000):
print('worker thread id: {}'.format(QtCore.QThread.currentThreadId()))
for x in xrange(m):
#y = math.sin(x)
y = x**2
time.sleep(0.001) # Weird, plotting stops if this is not present...
self.q.put((x,y,y))
print('Worker finished')
self.termino.emit()
class MainWindow(QtGui.QWidget):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.q = Queue()
self.termino = False
self.worker = Worker(self.q)
self.workerThread = None
self.btn = QtGui.QPushButton('Start worker')
self.pw = pg.PlotWidget(self)
pi = self.pw.getPlotItem()
pi.enableAutoRange('x', True)
pi.enableAutoRange('y', True)
self.ge1 = pi.plot(pen='y')
self.xs = []
self.ys = []
layout = QtGui.QVBoxLayout(self)
layout.addWidget(self.pw)
layout.addWidget(self.btn)
self.resize(400, 400)
def run(self):
self.workerThread = QtCore.QThread()
self.worker.moveToThread(self.workerThread)
self.worker.termino.connect(self.setTermino)
# moveToThread doesn't work here
self.btn.clicked.connect(partial(self.worker.run, 30000))
# moveToThread will work here
# assume def worker.run(self): instead of def worker.run(self, m=30000)
# self.btn.clicked.connect(self.worker.run)
self.btn.clicked.connect(self.graficar)
self.workerThread.start()
self.show()
def setTermino(self):
self.termino = True
def graficar(self):
if not self.q.empty():
e1,e2,ciclos = self.q.get()
self.xs.append(ciclos)
self.ys.append(e1)
self.ge1.setData(y=self.ys, x=self.xs)
if not self.termino:
QtCore.QTimer.singleShot(1, self.graficar)
if __name__ == '__main__':
app = QtGui.QApplication([])
window = MainWindow()
QtCore.QTimer.singleShot(0, window.run);
sys.exit(app.exec_())

The problem is that Qt attempts to choose the connection type (when you call signal.connect(slot)) based on the what thread the slot exists in. Because you have wrapped the slot in the QThread with partial, the slot you are connecting to resides in the MainThread (the GUI thread). You can override the connection type (as the second argument to connect() but that doesn't help because the method created by partial will always exist in the MainThread, and so setting the connection type to by Qt.QueuedConnection doesn't help.
The only way around this that I can see is to set up a relay signal, the sole purpose of which is to effectively change an emitted signal with no arguments (eg the clicked signal from a button) to a signal with one argument (your m parameter). This way you don't need to wrap the slot in the QThread with partial().
The code is below. I've created a signal with one argument (an int) called 'relay' in the main windows class. The button clicked signal is connected to a method within the main window class, and this method has a line of code which emits the custom signal I created. You can extend this method (relay_signal()) to get the integer to pass to the QThread as m (500 in this case), from where ever you like!
So here is the code:
from functools import partial
from Queue import Queue
import math
import sys
import time
class Worker(QtCore.QObject):
termino = pyqtSignal()
def __init__(self, q=None, parent=None):
super(Worker, self).__init__(parent)
self.q = q
def run(self, m=30000):
print('worker thread id: {}'.format(QtCore.QThread.currentThreadId()))
for x in xrange(m):
#y = math.sin(x)
y = x**2
#time.sleep(0.001) # Weird, plotting stops if this is not present...
self.q.put((x,y,y))
print('Worker finished')
self.termino.emit()
class MainWindow(QtGui.QWidget):
relay = pyqtSignal(int)
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.q = Queue()
self.termino = False
self.worker = Worker(self.q)
self.workerThread = None
self.btn = QtGui.QPushButton('Start worker')
self.pw = pg.PlotWidget(self)
pi = self.pw.getPlotItem()
pi.enableAutoRange('x', True)
pi.enableAutoRange('y', True)
self.ge1 = pi.plot(pen='y')
self.xs = []
self.ys = []
layout = QtGui.QVBoxLayout(self)
layout.addWidget(self.pw)
layout.addWidget(self.btn)
self.resize(400, 400)
def run(self):
self.workerThread = QtCore.QThread()
self.worker.termino.connect(self.setTermino)
self.worker.moveToThread(self.workerThread)
# moveToThread doesn't work here
# self.btn.clicked.connect(partial(self.worker.run, 30000))
# moveToThread will work here
# assume def worker.run(self): instead of def worker.run(self, m=30000)
#self.btn.clicked.connect(self.worker.run)
self.relay.connect(self.worker.run)
self.btn.clicked.connect(self.relay_signal)
self.btn.clicked.connect(self.graficar)
self.workerThread.start()
self.show()
def relay_signal(self):
self.relay.emit(500)
def setTermino(self):
self.termino = True
def graficar(self):
if not self.q.empty():
e1,e2,ciclos = self.q.get()
self.xs.append(ciclos)
self.ys.append(e1)
self.ge1.setData(y=self.ys, x=self.xs)
if not self.termino or not self.q.empty():
QtCore.QTimer.singleShot(1, self.graficar)
if __name__ == '__main__':
app = QtGui.QApplication([])
window = MainWindow()
QtCore.QTimer.singleShot(0, window.run);
sys.exit(app.exec_())
I also modified the graficar method to continue plotting (even after the thread is terminated) if there is still data in the queue. I think this might be why you needed the time.sleep in the QThread, which is now also removed.
Also regarding your comments in the code on where to place moveToThread, where it is now is correct. It should be before the call that connects the QThread slot to a signal, and the reason for this is discussed in this stack-overflow post: PyQt: Connecting a signal to a slot to start a background operation

Concurrent to QLabel in PyQt

I have i python application, which uses PyQt GUI. It application has some I/O operations, which i want to run in separate threads.
When each thread started, it should write messages to applications main window status bar and when last thread is completed, status bar messages should be cleared.
How can i handle number of threads via QThread?
Here is example of code:
import sys, time
from PyQt4 import QtCore, QtGui
from functools import partial
def io_emulator(sleep_seconds):
print 'We will sleep for %s seconds' % str(sleep_seconds)
time.sleep(sleep_seconds)
class IOThread(QtCore.QThread):
def __init__(self, func):
QtCore.QThread.__init__(self)
self.io_func = func
def run(self):
self.io_func()
class m_Window(QtGui.QWidget):
def __init__(self):
super(m_Window, self).__init__()
self.initUI()
def initUI(self):
self.thread_button = QtGui.QPushButton("Thread", self)
self.thread_button.move(30, 10)
self.spinbox = QtGui.QSpinBox(self)
self.spinbox.move(30, 50)
self.stat_label = QtGui.QLabel("", self)
self.stat_label.setGeometry(QtCore.QRect(200, 200, 150, 14))
self.stat_label.move(30,90)
self.setWindowTitle('Threads')
self.show()
self.thread_button.clicked.connect(self._sleeper)
def _sleeper(self):
seconds = int(self.spinbox.text())
stat_str = 'Sleeping %s seconds' % str(seconds)
io_func = partial(io_emulator, seconds)
set_status_f = partial(self.set_status_msg, stat_str)
self.thread = IOThread(io_func)
self.thread.started.connect(set_status_f)
self.thread.finished.connect(self.clear_status_msg)
self.thread.start()
def set_status_msg(self, msg):
self.stat_label.setText(msg)
def clear_status_msg(self):
self.stat_label.clear()
def main():
app = QtGui.QApplication(sys.argv)
m = m_Window()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
I want, that message is being cleared only when last thread is ended.

You cannot call QWidget functions from any thread but the main thread. If you want another thread to trigger GUI operations, then they should be communicated by emitting signals that are connected to your main thread:
def someFunc():
return "message"
class IOThread(QtCore.QThread):
statusUpdate = QtCore.pyqtSignal(str)
def __init__(self, func):
QtCore.QThread.__init__(self)
self.io_func = func
def run(self):
msg = self.io_func()
self.statusUpdate.emit(msg)
Then in your main thread, connect the io thread to the status label or some intermediate handler:
io_thread = IOThread(someFunc)
io_thread.statusUpdate.connect(self.status_label.setText)
This will create a queued connection, which places the call into the event loop of the main thread for execution.