如何在PyQt5中为QGridLayout添加stretch？

from PyQt5.QtWidgets import QApplication, QWidget, QGridLayout, QLabel

if __name__ == '__main__':
    app = QApplication([])
    window = QWidget()

    grid_layout = QGridLayout(window)

    label1 = QLabel("Label 1")
    grid_layout.addWidget(label1, 0, 0)

    label2 = QLabel("Label 2")
    grid_layout.addWidget(label2, 1, 0)

    label3 = QLabel("Label 3")
    grid_layout.addWidget(label3, 2, 0)

    # 添加stretch
    grid_layout.setColumnStretch(1, 1)
    grid_layout.setRowStretch(3, 1)

    window.setLayout(grid_layout)
    window.show()

    app.exec_()