Python QDialog未从主窗口打开（pyQt）

我试图通过单击主窗口中的一个按钮来启动一个对话框：下面是（qtdesigner生成的）代码，我只是为了测试它而对其进行了修改。。我已将showDial功能设置为在单击按钮时显示刻度盘。但它不起作用：

from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    _fromUtf8 = lambda s: s



class Ui_Dialog(object):
    def setupUi(self, Dialog):
        Dialog.setObjectName(_fromUtf8("Dialog"))
        Dialog.setWindowModality(QtCore.Qt.WindowModal)
        Dialog.resize(400, 300)
        Dialog.setWindowTitle(QtGui.QApplication.translate("Dialog", "Dialog", None,   QtGui.QApplication.UnicodeUTF8))

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

    def retranslateUi(self, Dialog):
        pass

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(309, 148)
        MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(50, 30, 191, 71))
        self.pushButton.setText(QtGui.QApplication.translate("MainWindow", "Open Dialog", None, QtGui.QApplication.UnicodeUTF8))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        MainWindow.setCentralWidget(self.centralwidget)

        self.retranslateUi(MainWindow)

        QtCore.QObject.connect(self.pushButton, QtCore.SIGNAL(_fromUtf8("clicked(QAbstractButton*)")), self.showDial)

        QtCore.QMetaObject.connectSlotsByName(MainWindow)



    def retranslateUi(self, MainWindow):
        pass

    def showDial(self):
      Dialog = QtGui.QDialog()
      u = Ui_Dialog()
      u.setupUi(Dialog)

      Dialog.exec_()


if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

---

信号连接有误，应为：

QtCore.QObject.connect(self.pushButton, QtCore.SIGNAL(_fromUtf8("clicked()")), self.showDial)

或者对于PyQt 4.5+，使用更具pythonic的方式：

self.pushButton.clicked.connect(self.showDial)