PySide Signals and Slots with QThread example

Posted by Matteo Mattei / 28th August 2011

In these days I started studying PySide. After some days spent in reading lot of stuff, I thought that a real example could be useful for who intends to start learning PySide as well. In this example I can show you how you can implement a custom signal (MySignal) together with the usage of threads with QThread.

The following code creates a window with two button: the first starts and stop a thread (MyThread) that runs a batch that prints a point in the stdout every seconds continuously. The second button lets you only start another thread (MyLongThread) that prints an asterisk in the stdout every second for 10 seconds.

This example uses the api version 2 (introduced with PyQt 4.5) to connect signals to slots.

#!/usr/bin/env python2

import sys, time
from PySide.QtGui import *
from PySide.QtCore import *

class MySignal(QObject):
	sig = Signal(str)

class MyLongThread(QThread):
	def __init__(self, parent = None):
		QThread.__init__(self, parent)
		self.exiting = False
		self.signal = MySignal()

	def run(self):
		end = time.time()+10
		while self.exiting==False:
			sys.stdout.write('*')
			sys.stdout.flush()
			time.sleep(1)
			now = time.time()
			if now>=end:
				self.exiting=True
		self.signal.sig.emit('OK')

class MyThread(QThread):
	def __init__(self, parent = None):
		QThread.__init__(self, parent)
		self.exiting = False

	def run(self):
		while self.exiting==False:
			sys.stdout.write('.')
			sys.stdout.flush()
			time.sleep(1)

class MainWindow(QMainWindow):
	def __init__(self, parent=None):
		QMainWindow.__init__(self,parent)
		self.centralwidget = QWidget(self)
		self.batchbutton = QPushButton('Start batch',self)
		self.longbutton = QPushButton('Start long (10 seconds) operation',self)
		self.label1 = QLabel('Continuos batch')
		self.label2 = QLabel('Long batch')
		self.vbox = QVBoxLayout()
		self.vbox.addWidget(self.batchbutton)
		self.vbox.addWidget(self.longbutton)
		self.vbox.addWidget(self.label1)
		self.vbox.addWidget(self.label2)
		self.setCentralWidget(self.centralwidget)
		self.centralwidget.setLayout(self.vbox)
		self.thread = MyThread()
		self.longthread = MyLongThread()
		self.batchbutton.clicked.connect(self.handletoggle)
		self.longbutton.clicked.connect(self.longoperation)
		self.thread.started.connect(self.started)
		self.thread.finished.connect(self.finished)
		self.thread.terminated.connect(self.terminated)
		self.longthread.signal.sig.connect(self.longoperationcomplete)

	def started(self):
		self.label1.setText('Continuous batch started')

	def finished(self):
		self.label1.setText('Continuous batch stopped')

	def terminated(self):
		self.label1.setText('Continuous batch terminated')

	def handletoggle(self):
		if self.thread.isRunning():
			self.thread.exiting=True
			self.batchbutton.setEnabled(False)
			while self.thread.isRunning():
				time.sleep(0.01)
				continue
			self.batchbutton.setText('Start batch')
			self.batchbutton.setEnabled(True)
		else:
			self.thread.exiting=False
			self.thread.start()
			self.batchbutton.setEnabled(False)
			while not self.thread.isRunning():
				time.sleep(0.01)
				continue
			self.batchbutton.setText('Stop batch')
			self.batchbutton.setEnabled(True)

	def longoperation(self):
		if not self.longthread.isRunning():
			self.longthread.exiting=False
			self.longthread.start()
			self.label2.setText('Long operation started')
			self.longbutton.setEnabled(False)

	def longoperationcomplete(self,data):
		self.label2.setText('Long operation completed with: '+data)
		self.longbutton.setEnabled(True)

if __name__=='__main__':
	app = QApplication(sys.argv)
	window = MainWindow()
	window.show()
	sys.exit(app.exec_())

For more information you can look at:
QThread documentation: http://doc.qt.nokia.com/latest/qthread.html
PySide signals and slots: http://developer.qt.nokia.com/wiki/Signals_and_Slots_in_PySide
PyQt api 2 on PySide: http://www.pyside.org/docs/pseps/psep-0101.html