python - What the error when I close the dialog

Question

I'm just learning PyQt and I have a small application that seems to work ok unit I hit the X in the upper right corner of the dialog box to close it down. When I do that and return to the console I see that an exception has been raised as follows:

To exit: use 'exit', 'quit', or Ctrl-D.
An exception has occurred, use %tb to see the full traceback.

SystemExit: 0


In [2]: %tb
Traceback (most recent call last):

  File "<ipython-input-1-4524246fa84a>", line 1, in <module>
    runfile('C:/Users/21025/simpleAdder.pyw', wdir='C:/Users/21025')

  File "C:Users21035AppDataLocalContinuumAnacondalibsite-packagesspyderlibwidgetsexternalshellsitecustomize.py", line 586, in runfile
    execfile(filename, namespace)

  File "C:/Users/21035/simpleAdder.pyw", line 81, in <module>
    sys.exit(app.exec_())

SystemExit: 0

What am I doing wrong ? Code for the application is shown below:

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_Dialog(object):
    def setupUi(self, Dialog):
        Dialog.setObjectName(_fromUtf8("Dialog"))
        Dialog.resize(673, 565)
        self.v1Input = QtGui.QLineEdit(Dialog)
        self.v1Input.setGeometry(QtCore.QRect(50, 70, 71, 20))
        self.v1Input.setObjectName(_fromUtf8("v1Input"))
        self.v2Input = QtGui.QLineEdit(Dialog)
        self.v2Input.setGeometry(QtCore.QRect(150, 70, 71, 20))
        self.v2Input.setObjectName(_fromUtf8("v2Input"))
        self.v3Input = QtGui.QLineEdit(Dialog)
        self.v3Input.setGeometry(QtCore.QRect(250, 70, 71, 20))
        self.v3Input.setObjectName(_fromUtf8("v3Input"))
        self.calc_result = QtGui.QLineEdit(Dialog)
        self.calc_result.setGeometry(QtCore.QRect(420, 70, 113, 20))
        self.calc_result.setObjectName(_fromUtf8("calc_result"))
        self.label = QtGui.QLabel(Dialog)
        self.label.setGeometry(QtCore.QRect(60, 50, 46, 13))
        self.label.setObjectName(_fromUtf8("label"))
        self.label_2 = QtGui.QLabel(Dialog)
        self.label_2.setGeometry(QtCore.QRect(160, 50, 46, 13))
        self.label_2.setObjectName(_fromUtf8("label_2"))
        self.label_3 = QtGui.QLabel(Dialog)
        self.label_3.setGeometry(QtCore.QRect(260, 50, 46, 13))
        self.label_3.setObjectName(_fromUtf8("label_3"))
        self.label_4 = QtGui.QLabel(Dialog)
        self.label_4.setGeometry(QtCore.QRect(450, 50, 46, 13))
        self.label_4.setObjectName(_fromUtf8("label_4"))
        self.pushButton = QtGui.QPushButton(Dialog)
        self.pushButton.setGeometry(QtCore.QRect(200, 230, 75, 23))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))

        self.retranslateUi(Dialog)
        QtCore.QObject.connect(self.pushButton, QtCore.SIGNAL(_fromUtf8("clicked()")), self.v1Input.clear)
        QtCore.QObject.connect(self.pushButton, QtCore.SIGNAL(_fromUtf8("clicked()")), self.v2Input.clear)
        QtCore.QObject.connect(self.pushButton, QtCore.SIGNAL(_fromUtf8("clicked()")), self.v3Input.clear)
        QtCore.QMetaObject.connectSlotsByName(Dialog)


    def retranslateUi(self, Dialog):
        Dialog.setWindowTitle(_translate("Dialog", "Dialog", None))
        self.label.setText(_translate("Dialog", "Val 1", None))
        self.label_2.setText(_translate("Dialog", "Val 2", None))
        self.label_3.setText(_translate("Dialog", "Val 3", None))
        self.label_4.setText(_translate("Dialog", "Result", None))
        self.pushButton.setText(_translate("Dialog", "Clear Inputs", None))       


if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    Dialog = QtGui.QDialog()
    ui = Ui_Dialog()
    ui.setupUi(Dialog)
    Dialog.show()
    sys.exit(app.exec_())

Answer 1

As the message suggests, the code includes sys.exit(app.exec_()), which will execute the GUI, and then call the exit routine. You called this from an interactive prompt, and so instead of quitting, it informed you that you tried to quit from within the thing you called. If you want to be able to call this code from an interactive prompt without the error, simply remove the exit part, change sys.exit(app.exec_()) to app.exec_().