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"""
This sample shows how to separate QApplication event loop from main thread.
This method works only on Linux. On Windows, you will see this app's window freezing.
"""
import logging
import threading
import sys
import time
from PyQt5.QtCore import QRect
from PyQt5.QtWidgets import (QApplication, QWidget)

#logging settings
logger = logging.getLogger(__name__); logger.setLevel(logging.DEBUG)	#output DEBUG or higher level messages
handler = logging.StreamHandler(); handler.setLevel(logging.DEBUG)
handler.setFormatter(logging.Formatter('%(asctime)s - %(name)s - %(threadName)s - %(levelname)s: %(message)s'))
logger.addHandler(handler)

class MainWindow(QWidget):
	"""main window class"""
	def __init__(self):
		super().__init__()
		self.setWindowTitle('Main Window')
		self.setGeometry(QRect(300,300, 200,150))

def ui_thread(app):
	"""a thread for QApplication event loop"""
	logger.debug("I'm UI thread.")
	app[0] = QApplication(sys.argv)
	app[0].exec_()

if __name__ == '__main__':
	logger.debug("I'm main thread.")

	#Qreate QApplication instance and start event loop.
	app = [None]
	ui_th = threading.Thread(target=ui_thread, args=(app,))
	ui_th.start()
	time.sleep(0.05)	#Wait for a short time to ensure QApplication instance created.

	#From now, you can do anything you like!
	w = MainWindow()
	w.show()

	time.sleep(1.5)
	w.setGeometry(QRect(300,300, 400,300))
	w.setWindowTitle("Size changed!")

	time.sleep(1.5)
	w.setWindowTitle("Title changed!!!!!!!!!!!!!!!!!!!!!!!!!!!")

	time.sleep(2)
	app[0].quit()	#end UI thread
	quit()	#end main thread