PyQt5 在 QGridLayout 中动态将小部件扩展为两列？

下面的示例是我根据Pyqt5 网格扩展小部件中的答案修改的，其开头如下：

然后，当您单击“列封面”按钮时，第一个标签“第 0 行，第 0 列”（以红色勾勒出）会在 QGridLayout 的两列上展开 - 但是，我得到了这样的信息：

因此，为了使轮廓标签居中，似乎考虑了两个网格列的宽度，这很好 - 但是，轮廓标签并没有扩展以占据两列的总宽度。

单击“列覆盖”按钮时，如何让标签扩展宽度并占据网格布局中两列的空间？即，我希望在程序启动后第一次单击按钮后获得此信息（在图像编辑器中编辑，框大约是我认为轮廓下方两个标签的边界框的并集​​）。

请注意，我知道我可以通过操纵来做到这一点.setFixedWidth-MainUi.label但是，我正在寻找某种设置，其中标签会自动扩展以填充可用宽度，具体取决于它是放置在 QGridLayout 的一列还是两列中。

代码：

import sys
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
from PyQt5 import QtCore, QtGui, QtWidgets

#rom example import Ui_MainWindow
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(191, 136)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.gridLayout = QtWidgets.QGridLayout(self.centralwidget)
        self.gridLayout.setObjectName("gridLayout")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setObjectName("pushButton")
        self.gridLayout.addWidget(self.pushButton, 0, 0, 1, 2)
        self.label_3 = QtWidgets.QLabel(self.centralwidget)
        self.label_3.setObjectName("label_3")
        self.gridLayout.addWidget(self.label_3, 3, 0, 1, 1)
        self.label_4 = QtWidgets.QLabel(self.centralwidget)
        self.label_4.setObjectName("label_4")
        self.gridLayout.addWidget(self.label_4, 2, 1, 1, 1)
        self.label_5 = QtWidgets.QLabel(self.centralwidget)
        self.label_5.setObjectName("label_5")
        self.gridLayout.addWidget(self.label_5, 3, 1, 1, 1)
        self.label_6 = QtWidgets.QLabel(self.centralwidget)
        self.label_6.setObjectName("label_6")
        self.gridLayout.addWidget(self.label_6, 1, 1, 1, 1)
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setObjectName("label")
        self.gridLayout.addWidget(self.label, 1, 0, 1, 1)
        self.label.setStyleSheet("border: 1px solid; border-color:red;")

        self.label_2 = QtWidgets.QLabel(self.centralwidget)
        self.label_2.setObjectName("label_2")
        self.gridLayout.addWidget(self.label_2, 2, 0, 1, 1)
        MainWindow.setCentralWidget(self.centralwidget)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "Column Cover"))
        self.label_3.setText(_translate("MainWindow", "Row 2, Column 0"))
        self.label_4.setText(_translate("MainWindow", "Row 1, Column 1"))
        self.label_5.setText(_translate("MainWindow", "Row 2, Column 1"))
        self.label_6.setText(_translate("MainWindow", "Row 0, Column 1"))
        self.label.setText(_translate("MainWindow", "Row 0, Column 0"))
        self.label_2.setText(_translate("MainWindow", "Row 1 ,Column 0 "))


class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        QWidget.__init__(self, parent)
        self.MainUi = Ui_MainWindow()
        self.MainUi.setupUi(self)

        self.MainUi.pushButton.setCheckable(True)                           # +++ True
        self.MainUi.pushButton.clicked.connect(self.expand_row)


    def expand_row(self, state):                                            # +++ state
        if state:
            self.MainUi.label_6.hide()
            self.MainUi.gridLayout.addWidget(self.MainUi.label, 1, 0, 1, 2, Qt.AlignHCenter) #  ...2, 1)
        else:
            self.MainUi.gridLayout.addWidget(self.MainUi.label, 1, 0, 1, 1) #  ...1, 1)
            self.MainUi.label_6.show()

#        self.MainUi.gridLayout.setRowStretch(0,1)


if __name__ == "__main__":
    app = QApplication(sys.argv)
    MainWindow = MainWindow()
    MainWindow.setWindowTitle('Example')
    MainWindow.show()
    sys.exit(app.exec_())