I have the following code

from PyQt5 import QtCore, QtGui, QtWidgets
from mw import Ui_MainWindow as mwin
from wd import Ui_Form as wdg

class widget(QtWidgets.QWidget):
    def __init__(self,parent = None):
            super(widget,self).__init__(parent)
            self.ui = wdg()
            self.ui.setupUi(self)
            self.show()

class Main(QtWidgets.QMainWindow):
    def __init__(self,parent = None):
        super(Main,self).__init__(parent)
        self.ui = mwin()
        self.ui.setupUi(self)
        self.show()
        w = widget(self)
import sys
if __name__ == '__main__':
        app = QtWidgets.QApplication(sys.argv)
        mn = Main()
        sys.exit(app.exec_())

The Ui is generated by qt designer and is imported from another file.

When I run the code, both the Main window and widget are merged together and a segmentation fault occurs when I close the Main window.

When I set the parent in the widget as None the problem goes but the widget has no parent.

I am unable to understand what is wrong and how to correctly set the Main window as the parent of the widget ?