pyqt5通过文本对话框打开文件

点击按钮，打开文本对话框，找一人文件，打开并显示内容                                                                                                                                                                                     

                                                                                                                                                                                              QFIleDialog

def openfile(self):
    filename,_ = QFileDialog.getOpenFileName(self);
    text=open(filename,‘r‘).read()
    self.textEdit.setText(text)

我用QFile,QTextStream,QIODevice做了半天也没做出来，改用python自带的文件操作命令做了出来。