如何在QGridLayout中重置小工具的列跨度？

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

class MyWidget(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        gridLayout = QGridLayout()
        self.setLayout(gridLayout)

        label1 = QLabel("Label 1")
        label2 = QLabel("Label 2")
        label3 = QLabel("Label 3")
        label4 = QLabel("Label 4")

        gridLayout.addWidget(label1, 0, 0)
        gridLayout.addWidget(label2, 0, 1)
        gridLayout.addWidget(label3, 1, 0)
        gridLayout.addWidget(label4, 1, 1)

        # 设置label2的列跨度为2
        gridLayout.setColumnSpan(label2, 2)

        self.setWindowTitle("QGridLayout Span Example")
        self.setGeometry(300, 300, 300, 200)
        self.show()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    widget = MyWidget()
    sys.exit(app.exec_())