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How to create a QDialog without blocking main thread in PyQt5?

Say you have MainWindow in PyQt5 and as part of this app you need a custom Pop-up/Dialog box that does not block MainWindow thread.

To do this, you first design your dialog box in PyQt5 Designer and save it as a UI file and then compile using pyuic5 as follows:

pyuic5 dialog.ui -o dialog.py

This will result into a python script under dialog.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'dialog.ui'
# Created by: PyQt5 UI code generator 5.15.4
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_Dialog(object):
    def setupUi(self, Dialog):
        Dialog.resize(400, 300)
        self.label = QtWidgets.QLabel(Dialog)
        self.label.setGeometry(QtCore.QRect(10, 110, 371, 20))


    def retranslateUi(self, Dialog):
        _translate = QtCore.QCoreApplication.translate
        Dialog.setWindowTitle(_translate("Dialog", "Dialog"))
        self.label.setText(_translate("Dialog", "Welcome to Neehack"))

Note: as recommended by many PyQt5 forms, never modify PyQt5 Designer class. If you need to add features that are only available through python, then create a separate class and call PyQt5 Designer class in your external class as below.

External class calling Ui_Dialog

class CustomDialog(QDialog, Ui_dialog):
    def __init__(self):


    def run(self):
        print("Welcome to https://neehack.com/")

Make sure to avoid calling `self.exec_()` in this class, if you do so it would block the main thread until this dialog box is closed as explained in documentation:

Shows the dialog as a modal dialog, blocking until the user closes it. The function returns a DialogCode result.

If you just use `self.show(), this will create a non-modeled dialog box and save it in memory which you will have to keep a reference of until you want the dialog box to exist. If you wanted to hide the dialog box, you can just use self.hide()

Finally call your custom dialog box class in your MainWindow class as below:

def buttonClicked(self):
     self.customDialog = CustomDialog()

Remember to use self while referencing your variable, otherwise as soon as the buttonClicked function is done, the dialog box will be moved to python recycle bin, destroying dialog box.

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