PyQt Thread Completes and outputs same message twice - pyqt

Question

I'm trying to create a play/pause/resume/ button with a progress bar. User presses 'Start' and the progress bar initializes and a pause/resume button populates. Once the progress completes, a message is printed and the pause/resume buttons are hidden while the 'Start' button is shown again. However, when I try to run 'Start' again, it prints the same completion message an additional time.
If I run it twice, it prints out two completion messages. Run it three times, prints out three completion messages and etc.
from PyQt5.QtWidgets import (
QWidget, QApplication, QProgressBar, QMainWindow,
QHBoxLayout, QPushButton
)
from PyQt5.QtCore import (
Qt, QObject, pyqtSignal, pyqtSlot, QRunnable, QThreadPool
)
import time
class WorkerSignals(QObject):
progress = pyqtSignal(int)
finished = pyqtSignal()
class JobRunner(QRunnable):
signals = WorkerSignals()
def __init__(self):
super().__init__()
self.is_paused = False
self.is_killed = False
#pyqtSlot()
def run(self):
for n in range(100):
self.signals.progress.emit(n + 1)
time.sleep(0.001)
while self.is_paused:
time.sleep(0)
if self.is_killed:
break
self.signals.finished.emit()
def finished(self):
print('Finished')
def pause(self):
self.is_paused = True
def resume(self):
self.is_paused = False
# def kill(self):
class MainWindow(QMainWindow):
def __init__(self):
super().__init__()
# Some buttons
self.w = QWidget()
self.l = QHBoxLayout()
self.w.setLayout(self.l)
self.btn_start = QPushButton("Start")
self.l.addWidget(self.btn_start)
self.setCentralWidget(self.w)
# Create a statusbar.
self.status = self.statusBar()
self.progress = QProgressBar()
self.status.addPermanentWidget(self.progress)
# Thread runner
# self.threadpool = QThreadPool()
# # Create a runner
# self.runner = JobRunner()
# self.runner.signals.progress.connect(self.update_progress)
# self.threadpool.start(self.runner)
self.btn_start.pressed.connect(self.start_runner)
# btn_pause.pressed.connect(self.runner.pause)
# btn_resume.pressed.connect(self.runner.resume)
# self.startTestSignal.connect(self.update_progress)
self.show()
def update_progress(self, n):
self.progress.setValue(n)
def start_runner(self):
# Create ThreadPool
self.threadpool = QThreadPool()
self.threadpool.clear()
# Create a runner
self.runner = JobRunner()
self.runner.signals.progress.connect(self.update_progress)
self.threadpool.start(self.runner)
self.progress.setValue(0)
# Change Start Button to Pause
self.btn_start.hide()
# self.btn_start.setEnabled(False)
self.btn_pause = QPushButton("Pause")
self.btn_resume = QPushButton("Resume")
self.l.addWidget(self.btn_pause)
self.l.addWidget(self.btn_resume)
self.btn_pause.pressed.connect(self.runner.pause)
self.btn_resume.pressed.connect(self.runner.resume)
self.runner.signals.finished.connect(self.check)
def check(self):
print('Thread Done')
self.btn_start.show()
self.progress.setValue(0)
# self.runner.terminate()
self.btn_pause.hide()
self.btn_resume.hide()
app = QApplication([])
w = MainWindow()
app.exec_()

Answer 1

You are creating a WorkerSignals as a class attribute, making it a persistent for the class; so when you do this:
self.runner.signals.finished.connect(self.check)
you are actually connecting again to signals.finished, and when you emit the signal the function self.check is called each time the signal has been connected.
The solution is to create the WorkerSignals as an instance attribute:
class JobRunner(QRunnable):
def __init__(self):
super().__init__()
self.signals = WorkerSignals()
self.is_paused = False
self.is_killed = False