Getting a blank form when running PyQt application

Question

I wrote a small PyQt program based on an example from a book. I edited the code to add some niceties. Below is my code:

from __future__ import division
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
import sys
class Ui_MainWindow(QWidget):
    def __init__(self):
        QWidget.__init__(self)
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayoutWidget = QtWidgets.QWidget(self.centralwidget)
        self.verticalLayoutWidget.setGeometry(QtCore.QRect(9, 9, 781, 461))
        self.verticalLayoutWidget.setObjectName("verticalLayoutWidget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.verticalLayoutWidget)
        self.verticalLayout.setObjectName("verticalLayout")
        self.textBrowser = QtWidgets.QTextBrowser(self.verticalLayoutWidget)
        self.textBrowser.setObjectName("textBrowser")
        self.verticalLayout.addWidget(self.textBrowser)
        self.horizontalLayoutWidget = QtWidgets.QWidget(self.centralwidget)
        self.horizontalLayoutWidget.setGeometry(QtCore.QRect(10, 480, 781, 80))
        self.horizontalLayoutWidget.setObjectName("horizontalLayoutWidget")
        self.horizontalLayout_2 = QtWidgets.QHBoxLayout(self.horizontalLayoutWidget)
        self.horizontalLayout_2.setObjectName("horizontalLayout_2")
        self.label = QtWidgets.QLabel(self.horizontalLayoutWidget)
        font = QtGui.QFont()
        font.setPointSize(16)
        self.label.setFont(font)
        self.label.setObjectName("label")
        self.horizontalLayout_2.addWidget(self.label)
        self.lineEdit = QtWidgets.QLineEdit(self.horizontalLayoutWidget)
        self.lineEdit.setBaseSize(QtCore.QSize(0, 0))
        font = QtGui.QFont()
        font.setPointSize(12)
        self.lineEdit.setFont(font)
        self.lineEdit.setText("")
        self.lineEdit.setObjectName("lineEdit")
        self.horizontalLayout_2.addWidget(self.lineEdit)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 21))
        self.menubar.setObjectName("menubar")
        self.menuFile = QtWidgets.QMenu(self.menubar)
        self.menuFile.setObjectName("menuFile")
        MainWindow.setMenuBar(self.menubar)
        self.actionQuit = QtWidgets.QAction(MainWindow)
        self.actionQuit.setObjectName("actionQuit")
        self.menuFile.addAction(self.actionQuit)
        self.menubar.addAction(self.menuFile.menuAction())

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

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setText(_translate("MainWindow", "Expression:"))
        self.menuFile.setTitle(_translate("MainWindow", "File"))
        self.actionQuit.setText(_translate("MainWindow", "Quit (Ctrl+Q)"))
        self.actionQuit.setShortcut(_translate("MainWindow", "Ctrl+Q"))
        self.lineEdit.setFocus()
        self.connect(self.lineEdit, self.updateUi)
        self.setWindowTitle("Calculate")
    def updateUi(self):
        try:
            text = unicode(self.lineEdit.text())
            self.browser.append("%s = <b>%s</b>" % (text,eval(text)))
        except:
            self.browser.append("<font color=red>Invalid Expression</font>")
if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = Ui_MainWindow()
    window.show()
    sys.exit(app.exec_())

Output:

But when I execute this file I only get a blank window without any widgets inside it. What is the error in my code?

Answer 1

You defined setupUi() function but I don't see you executing it anywhere. You should expand your __init__ with:

class Ui_MainWindow(QWidget):
    def __init__(self):
        QWidget.__init__(self)
        self.setupUi(your_main_window)