【求助】QSplitter分割器分割比例设定的问题

import sys
from PyQt5.QtWidgets import (QWidget, QHBoxLayout, QFrame,
                             QSplitter, QStyleFactory, QApplication)
from PyQt5.QtCore import Qt


class Example(QWidget):
    def __init__(self):
        super().__init__()

        self.initUI()

    def initUI(self):
        hbox = QHBoxLayout(self)

        topleft = QFrame(self)
        topleft.setFrameShape(QFrame.StyledPanel)

        topmid = QFrame(self)
        topmid.setFrameShape(QFrame.StyledPanel)

        topright = QFrame(self)
        topright.setFrameShape(QFrame.StyledPanel)

        bottom = QFrame(self)
        bottom.setFrameShape(QFrame.StyledPanel)

        # 通过QSplitter，用户可以拖动子控件边界来调整子控件的尺寸
        splitter1 = QSplitter(Qt.Horizontal)   # 水平方向宽度的调整
        splitter1.addWidget(topleft)           #  通过QSplitter需要至少两个控件
        splitter1.addWidget(topmid)
        splitter1.addWidget(topright)
        splitter1.setStretchFactor(0, 4)    #第一个参数是子控件的索引号，从0开始，第二个参数为比例。 下同
        splitter1.setStretchFactor(1, 3)
        splitter1.setStretchFactor(2, 2)

        #splitter2 = QSplitter(Qt.Horizontal)   #水平的可以一次添加多个控件，无需再次嵌套
        #splitter2.addWidget(splitter1)
        #splitter2.addWidget(topright)
        
        splitter2 = QSplitter(Qt.Vertical)     # 垂直方向宽度的调整
        splitter2.addWidget(splitter1)         #  QSplitter嵌套，后面的splitter的变化会影响前面splitter上所有控件的高度
        splitter2.addWidget(bottom)
        splitter2.setStretchFactor(0,1)
        splitter2.setStretchFactor(1,1)

        hbox.addWidget(splitter2)           # 由于已经进行了嵌套，所以只需要最后的splitter
        self.setLayout(hbox)

        self.setGeometry(300, 300, 300, 200)
        self.setWindowTitle('QSplitter')
        self.show()

    def onChanged(self, text):
        self.lbl.setText(text)
        self.lbl.adjustSize()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())