PySide自定义小部件不能自动适应QTableWidget

from PySide2.QtWidgets import QApplication, QMainWindow, QTableWidget, QTableWidgetItem

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        self.table_widget = QTableWidget(self)
        self.table_widget.setColumnCount(3)
        self.table_widget.setRowCount(3)
        self.table_widget.horizontalHeader().setSectionResizeMode(QTableWidget.Stretch)
        self.table_widget.verticalHeader().setSectionResizeMode(QTableWidget.Stretch)

        self.setCentralWidget(self.table_widget)

        self.populate_table()

    def populate_table(self):
        for row in range(self.table_widget.rowCount()):
            for column in range(self.table_widget.columnCount()):
                item = QTableWidgetItem(f"Row {row}, Column {column}")
                self.table_widget.setItem(row, column, item)

if __name__ == "__main__":
    app = QApplication([])
    window = MainWindow()
    window.show()
    app.exec_()