从 QtextEdit pyside2 导出 pdf打印按钮有效，但 pdf 没有保存在我的电脑中，它是空白的

如何解决从 QtextEdit pyside2 导出 pdf打印按钮有效，但 pdf 没有保存在我的电脑中，它是空白的

import sys
import platform
from pyside2 import QtCore,QtGui,QtWidgets
from pyside2.QtCore import (QCoreApplication,QPropertyAnimation,QDate,QDateTime,QMetaObject,QPoint,QRect,QSize,QTime,QUrl,QEvent)
from pyside2.QtGui import (QBrush,QColor,QConicalGradient,QCursor,QFont,QFontDatabase,QIcon,QKeySequence,QLinearGradient,QPainter,Qpixmap,QRadialGradient)
from pyside2.QtWidgets import *
from pyside2.QtCore import QFileInfo
from pyside2.QtPrintSupport import QPrinter

from ui_interface import Ui_MainWindow


class MainWindow(QMainWindow):
    def __init__(self):
        QMainWindow.__init__(self)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        self.ui.start_btn.clicked.connect(lambda: self.ui.textEdit.setText("Hello World"))
        self.ui.printbutton.clicked.connect(lambda: self.SavetoPDF())
        self.show()

    def SavetoPDF(self):
        filename = QFileDialog.getSaveFileName(self,'Save to PDF',None,'PDF files(.pdf);; All Files')
        if filename != "":
            if QFileInfo(filename).suffix() == "": filename += '.pdf'
            printer = QPrinter(QPrinter.HighResolution)
            printer.setoutputFormat(QPrinter.PdfFormat)
            printer.setoutputFileName(filename)
            print(self.ui.textEdit.document())


if __name__ == '__main__':
    app = QApplication(sys.argv)`
    window = MainWindow()
    sys.exit(app.exec_())