create a popup window using a pushbutton in PyQt5

popup.py

#create a popup window using a pushbutton in PyQt5
import sys

from PyQt5 import QtCore, QtWidgets

class Ui_FirstWindow(object) :
    def setupUi(self, FirstWindow) :
        FirstWindow.setObjectName("FirstWindow")
        FirstWindow.resize(400, 300)
        self.centralWidget = QtWidgets.QWidget(FirstWindow)
        self.centralWidget.setObjectName("centralWidget")
        self.pushButton = QtWidgets.QPushButton(self.centralWidget)
        self.pushButton.setGeometry(QtCore.QRect(110, 130, 191, 23))
        self.pushButton.setObjectName("pushButton")
        FirstWindow.setCentralWidget(self.centralWidget)

        self.retranslateUi(FirstWindow)
        QtCore.QMetaObject.connectSlotsByName(FirstWindow)

    def retranslateUi(self, MainWindow) :
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("FirstWindow", "FirstWindow"))
        self.pushButton.setText(_translate("FirstWindow", "LoadSecondWindow"))

    def LoadSecondWindow(self) :
        SecondWindow = QtWidgets.QMainWindow()
        ui = Ui_SecondWindow()
        ui.setupUi(SecondWindow)
        SecondWindow.show()


class Ui_SecondWindow(object) :

    def setupUi(self, SecondWindow) :
        SecondWindow.setObjectName("SecondWindow")
        SecondWindow.resize(400, 300)
        self.centralWidget = QtWidgets.QWidget(SecondWindow)
        self.centralWidget.setObjectName("centralWidget")
        self.pushButton = QtWidgets.QPushButton(self.centralWidget)
        self.pushButton.setGeometry(QtCore.QRect(110, 130, 191, 23))
        self.pushButton.setObjectName("pushButton")
        SecondWindow.setCentralWidget(self.centralWidget)

        self.retranslateUi(SecondWindow)
        QtCore.QMetaObject.connectSlotsByName(SecondWindow)

    def retranslateUi(self, MainWindow) :
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("SecondWindow", "SecondWindow"))
        self.pushButton.setText(_translate("SecondWindow", "Congratz !"))


class Controller :

    def __init__(self) :
        pass

    def Show_FirstWindow(self) :
        self.FirstWindow = QtWidgets.QMainWindow()
        self.ui = Ui_FirstWindow()
        self.ui.setupUi(self.FirstWindow)
        self.ui.pushButton.clicked.connect(self.Show_SecondWindow)

        self.FirstWindow.show()

    def Show_SecondWindow(self) :
        self.SecondWindow = QtWidgets.QMainWindow()
        self.ui = Ui_SecondWindow()
        self.ui.setupUi(self.SecondWindow)
        self.ui.pushButton.clicked.connect(self.Print)

        self.SecondWindow.show()

    def Print(self) :
        print('After 99 hours of trying out everything')


if __name__ == '__main__' :
    app = QtWidgets.QApplication(sys.argv)
    Controller = Controller()
    Controller.Show_FirstWindow()
    sys.exit(app.exec_())