pyqt5 getOpenFilename 函数总是出现bug，请问应该怎么更改？

class Ui_Second(object):

def setupUi(self, Dialog):

    Dialog.setObjectName("Secondwindow")
    Dialog.resize(1065, 791)
    Dialog.setSizeGripEnabled(True)
    self.label = QtWidgets.QLabel(Dialog)
    self.label.setGeometry(QtCore.QRect(70, 60, 81, 18))
    self.label.setObjectName("label")
    self.verticalLayoutWidget = QtWidgets.QWidget(Dialog)
    self.verticalLayoutWidget.setGeometry(QtCore.QRect(150, 230, 401, 371))
    self.verticalLayoutWidget.setObjectName("verticalLayoutWidget")
    self.verticalLayout = QtWidgets.QVBoxLayout(self.verticalLayoutWidget)
    self.verticalLayout.setContentsMargins(0, 0, 0, 0)
    self.verticalLayout.setObjectName("verticalLayout")
    self.label_3 = QtWidgets.QLabel(self.verticalLayoutWidget)
    self.label_3.setObjectName("label_3")
    self.verticalLayout.addWidget(self.label_3)
    self.label_4 = QtWidgets.QLabel(self.verticalLayoutWidget)
    self.label_4.setObjectName("label_4")
    self.verticalLayout.addWidget(self.label_4)
    self.label_6 = QtWidgets.QLabel(self.verticalLayoutWidget)
    self.label_6.setObjectName("label_6")
    self.verticalLayout.addWidget(self.label_6)
    self.label_5 = QtWidgets.QLabel(self.verticalLayoutWidget)
    self.label_5.setObjectName("label_5")
    self.verticalLayout.addWidget(self.label_5)
    self.label_2 = QtWidgets.QLabel(self.verticalLayoutWidget)
    self.label_2.setObjectName("label_2")
    self.verticalLayout.addWidget(self.label_2)
    self.verticalLayoutWidget_2 = QtWidgets.QWidget(Dialog)
    self.verticalLayoutWidget_2.setGeometry(QtCore.QRect(679, 230, 281, 371))
    self.verticalLayoutWidget_2.setObjectName("verticalLayoutWidget_2")
    self.verticalLayout_2 = QtWidgets.QVBoxLayout(self.verticalLayoutWidget_2)
    self.verticalLayout_2.setContentsMargins(0, 0, 0, 0)
    self.verticalLayout_2.setObjectName("verticalLayout_2")
    self.pushButton_2 = QtWidgets.QPushButton(self.verticalLayoutWidget_2)
    self.pushButton_2.setObjectName("pushButton_2")
    self.verticalLayout_2.addWidget(self.pushButton_2)
    self.pushButton_4 = QtWidgets.QPushButton(self.verticalLayoutWidget_2)
    self.pushButton_4.setObjectName("pushButton_4")
    self.verticalLayout_2.addWidget(self.pushButton_4)
    self.pushButton_5 = QtWidgets.QPushButton(self.verticalLayoutWidget_2)
    self.pushButton_5.setObjectName("pushButton_5")
    self.verticalLayout_2.addWidget(self.pushButton_5)
    self.pushButton_3 = QtWidgets.QPushButton(self.verticalLayoutWidget_2)
    self.pushButton_3.setObjectName("pushButton_3")
    self.verticalLayout_2.addWidget(self.pushButton_3)
    self.pushButton = QtWidgets.QPushButton(self.verticalLayoutWidget_2)
    self.pushButton.setObjectName("pushButton")
    self.verticalLayout_2.addWidget(self.pushButton)
    self.pushButton_6 = QtWidgets.QPushButton(Dialog)
    self.pushButton_6.setGeometry(QtCore.QRect(770, 640, 141, 81))
    self.pushButton_6.setObjectName("pushButton_6")

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



    self.pushButton_2.clicked.connect(self.openfile)

def openfile(self):
    filename,_ = QFileDialog.getOpenFileName(self, 'a');
    self.label_3.setText(filename)

错误是

参数不匹配，第一个参数应该是 parent，QWidget 类型，而不是 Ui_Second。