Python kernel dies for second run of PyQt5 GUI

Question

• Using Spyder in Python 3.5.2 |Anaconda 4.2.0 (64-bit) Windows package. qt: 5.6.0
• For first run, GUI window opens as expected
• For 2nd run, nothing opens, and receiving Kernel died, restarting log message.

gui1.py:

import sys from PyQt5.QtWidgets import QApplication, QWidget

app = QApplication(sys.argv)

w = QWidget()

w.resize(250,150) w.show()

#sys.exit(app.exec_()) 
app.exec_()

IPhython log:

runfile('F:/work/ws_python/TestProj1/gui1/gui1.py', wdir='F:/work/ws_python/TestProj1/gui1')

runfile('F:/work/ws_python/TestProj1/gui1/gui1.py', wdir='F:/work/ws_python/TestProj1/gui1')

Kernel died, restarting

Kernel died, restarting

Kernel died, restarting

Why kernel dies for 2nd run and how to solve it?

(Doing the same even using #sys.exit(app.exec_()) as last line.)

Answer 1

This code fixed the problem, thanks for the hint.

app = QtCore.QCoreApplication.instance()
if app is None:
    app = QtWidgets.QApplication(sys.argv)

Answer 2

This works better for the kernel died, restarting error.

from PyQt5.QtWidgets import QApplication, QDialog
from PyQt5.QtCore import QCoreApplication

#app = QApplication(sys.argv)
app = QCoreApplication.instance()
if app is None:
    app = QApplication(sys.argv)

Answer 3

For me the above solution worked but only as long as the window-close button (from the Window decoration) was used to close the main window. But the problem still was present when the program was terminated from a GUI signal handler, reacting e.g. to a button being clicked. After much fiddling, I learned that a safe enough way for terminating in this situation is as follows:

def safeExit(self):
    """exit the application gently so Spyder IDE will not hang"""
    self.ui.deleteLater()
    self.ui.close()
    self.ui.destroy()


... self.ui.Button2.clicked.connect(self.safeExit) ...