PyQt window closes immediately after opening

I am getting an issue when trying to open a PyQt window.

The code below is an example of my original code. When I imported the module in import Test and ran test.Start(), I got the following error:

QCoreApplication::exec: The event loop is already running

After some research, I found out it was because I had already already made a QApplication.

test.py....
import sys

def Start():
    app = QApplication(sys.argv)
    m = myWindow()
    m.show()
    app.exec_()

class myWindow():....

if __name__ == "__main__":
    Start()

So then I read that I could rewrite my code like this and it would fix the error:

test.py....

def Start():
    m = myWindow()
    m.show()


class myWindow():....

if __name__ == "__main__":
    import sys
    app = QApplication(sys.argv)
    Start()
    app.exec_()

Now I no longer get the QCoreApplication::exec: The event loop is already running error, but my window closes almost immediately after opening.

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

You need to keep a reference to the opened window, otherwise it goes out of scope and is garbage collected, which will destroy the underlying C++ object also. Try:

def Start():
    m = myWindow()
    m.show()
    return m


class myWindow():....

if __name__ == "__main__":
    import sys
    app = QApplication(sys.argv)
    window = Start()
    app.exec_()

Method 2

You can also do:

def Start():
    global m
    m = myWindow()
    m.show()

class myWindow():....

if __name__ == "__main__":
    import sys
    app = QApplication(sys.argv)
    window = Start()
    app.exec_()

Method 3

Use the following code. Your problem is in your imports and using “show” as a name for function as far as I assume. You haven’t provided what you have written in your class, so it’s difficult to guess. But following code works like a charm. 😉

Best wishes, good luck!

import sys
from PyQt5 import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *

app = QApplication(sys.argv)
def Start():
    m = myWindow()
    m.showWid()
    sys.exit(app.exec())

class myWindow:
  def __init__(self):
    self.window = QWidget()
    self.window.setWindowTitle("Program Title")
    self.window.setFixedWidth(600)
    self.window.setStyleSheet("background: #18BEBE;")

  def showWid(self):
    self.window.show()

if __name__ == "__main__":
    Start()

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0