Python-сообщество

 import sys
from MAIN import Ui_MainWindow
from PyQt5 import QtCore, QtGui,QtWidgets
from dialog3 import Ui_Dialog3
class Secwin(QtWidgets.QMainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        self.ui = Ui_Dialog3()
        self.ui.setupUi(self)
            
class main(QtWidgets.QMainWindow,Ui_MainWindow):
    def __init__(self,parent=None):
        QtWidgets.QMainWindow.__init__(self,parent)
        self.setupUi(self)
        self.pushButton.clicked.connect(self.open_win)
    def  open_win(self):
        child=Secwin(win1,QtWidgets.QtDialog)
        child.setWindowModality(QtWidgets.QtWindowMogal)
        print(child.windowType() == QtWidgets.Qt.Dialog)
        child.show()
            
if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    win1 = main()
    win1.show()
    sys.exit(app.exec_())