本文是对《Python Qt GUI快速编程》的第9章的堆叠窗口例子Vehicle Rental用Python3+PyQt5+Qt Designer进行改写。
第一部分无借用Qt Designer，完全用代码实现。
第二部分则借用Qt Designer，快速实现。

第一部分：

import sys
from PyQt5.QtCore import (Qt)
from PyQt5.QtWidgets import (QApplication, QComboBox, QDialog,
 QDialogButtonBox, QFrame, QGridLayout, QHBoxLayout, QLabel,
 QSpinBox, QStackedWidget, QVBoxLayout, QWidget)

class VehicleRentalDlg(QDialog):

 def __init__(self, parent=None):
 super(VehicleRentalDlg, self).__init__(parent)

 vehicleLabel = QLabel("&Vehicle Type:")
 self.vehicleComboBox = QComboBox()
 vehicleLabel.setBuddy(self.vehicleComboBox)
 self.vehicleComboBox.addItems(["Car", "Van"])
 colorLabel = QLabel("Co&lor:")
 self.colorComboBox = QComboBox()
 colorLabel.setBuddy(self.colorComboBox)
 self.colorComboBox.addItems(["Black", "Blue", "Green", "Red",
 "Silver", "White", "Yellow"])
 seatsLabel = QLabel("&Seats:")
 self.seatsSpinBox = QSpinBox()
 seatsLabel.setBuddy(self.seatsSpinBox)
 self.seatsSpinBox.setRange(2, 12)
 self.seatsSpinBox.setValue(4)
 self.seatsSpinBox.setAlignment(Qt.AlignRight|Qt.AlignVCenter)
 weightLabel = QLabel("&Weight:")
 self.weightSpinBox = QSpinBox()
 weightLabel.setBuddy(self.weightSpinBox)
 self.weightSpinBox.setRange(1, 8)
 self.weightSpinBox.setValue(1)
 self.weightSpinBox.setAlignment(Qt.AlignRight|Qt.AlignVCenter)
 self.weightSpinBox.setSuffix(" tons")
 volumeLabel = QLabel("Volu&me")
 self.volumeSpinBox = QSpinBox()
 volumeLabel.setBuddy(self.volumeSpinBox)
 self.volumeSpinBox.setRange(4, 22)
 self.volumeSpinBox.setValue(10)
 self.volumeSpinBox.setAlignment(Qt.AlignRight|Qt.AlignVCenter)
 self.volumeSpinBox.setSuffix(" cu m")
 mileageLabel = QLabel("Max. Mileage")
 self.mileageLabel = QLabel("1000 miles")
 self.mileageLabel.setAlignment(Qt.AlignRight|Qt.AlignVCenter)
 self.mileageLabel.setFrameStyle(QFrame.StyledPanel|QFrame.Sunken)
 self.buttonBox = QDialogButtonBox(QDialogButtonBox.Ok|
 QDialogButtonBox.Cancel)

 self.stackedWidget = QStackedWidget()
 carWidget = QWidget()
 carLayout = QGridLayout()
 carLayout.addWidget(colorLabel, 0, 0)
 carLayout.addWidget(self.colorComboBox, 0, 1)
 carLayout.addWidget(seatsLabel, 1, 0)
 carLayout.addWidget(self.seatsSpinBox, 1, 1)
 carWidget.setLayout(carLayout)
 self.stackedWidget.addWidget(carWidget)
 vanWidget = QWidget()
 vanLayout = QGridLayout()
 vanLayout.addWidget(weightLabel, 0, 0)
 vanLayout.addWidget(self.weightSpinBox, 0, 1)
 vanLayout.addWidget(volumeLabel, 1, 0)
 vanLayout.addWidget(self.volumeSpinBox, 1, 1)
 vanWidget.setLayout(vanLayout)
 self.stackedWidget.addWidget(vanWidget)

 topLayout = QHBoxLayout()
 topLayout.addWidget(vehicleLabel)
 topLayout.addWidget(self.vehicleComboBox)
 bottomLayout = QHBoxLayout()
 bottomLayout.addWidget(mileageLabel)
 bottomLayout.addWidget(self.mileageLabel)
 layout = QVBoxLayout()
 layout.addLayout(topLayout)
 layout.addWidget(self.stackedWidget)
 layout.addLayout(bottomLayout)
 layout.addWidget(self.buttonBox)
 self.setLayout(layout)


 self.buttonBox.accepted.connect(self.accept)
 self.buttonBox.rejected.connect(self.reject)
 self.vehicleComboBox.currentIndexChanged[str].connect(self.setWidgetStack)
 self.weightSpinBox.valueChanged[int].connect(self.weightChanged)

 self.setWindowTitle("Vehicle Rental")


 def setWidgetStack(self, text):
 if text == "Car":
 self.stackedWidget.setCurrentIndex(0)
 self.mileageLabel.setText("1000 miles")
 else:
 self.stackedWidget.setCurrentIndex(1)
 self.weightChanged(self.weightSpinBox.value())


 def weightChanged(self, amount):
 self.mileageLabel.setText("{0} miles".format(8000 / amount))


app = QApplication(sys.argv)
form = VehicleRentalDlg()
form.show()
app.exec_()

第二部分：
/home/yrd/eric_workspace/Vehicle/Ui_vehiclerentaldlg.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file '/home/yrd/eric_workspace/Vehicle/vehiclerentaldlg.ui'
#
# Created by: PyQt5 UI code generator 5.7
#
# WARNING! All changes made in this file will be lost!

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_VehicleRentalDlg(object):
 def setupUi(self, VehicleRentalDlg):
 VehicleRentalDlg.setObjectName("VehicleRentalDlg")
 VehicleRentalDlg.resize(206, 246)
 self.gridlayout = QtWidgets.QGridLayout(VehicleRentalDlg)
 self.gridlayout.setContentsMargins(9, 9, 9, 9)
 self.gridlayout.setSpacing(6)
 self.gridlayout.setObjectName("gridlayout")
 self.buttonBox = QtWidgets.QDialogButtonBox(VehicleRentalDlg)
 self.buttonBox.setOrientation(QtCore.Qt.Horizontal)
 self.buttonBox.setStandardButtons(QtWidgets.QDialogButtonBox.Cancel|QtWidgets.QDialogButtonBox.Ok)
 self.buttonBox.setObjectName("buttonBox")
 self.gridlayout.addWidget(self.buttonBox, 4, 0, 1, 1)
 spacerItem = QtWidgets.QSpacerItem(188, 16, QtWidgets.QSizePolicy.Minimum, QtWidgets.QSizePolicy.Expanding)
 self.gridlayout.addItem(spacerItem, 3, 0, 1, 1)
 self.hboxlayout = QtWidgets.QHBoxLayout()
 self.hboxlayout.setContentsMargins(0, 0, 0, 0)
 self.hboxlayout.setSpacing(6)
 self.hboxlayout.setObjectName("hboxlayout")
 self.label_6 = QtWidgets.QLabel(VehicleRentalDlg)
 self.label_6.setObjectName("label_6")
 self.hboxlayout.addWidget(self.label_6)
 self.mileageLabel = QtWidgets.QLabel(VehicleRentalDlg)
 self.mileageLabel.setFrameShape(QtWidgets.QFrame.StyledPanel)
 self.mileageLabel.setFrameShadow(QtWidgets.QFrame.Sunken)
 self.mileageLabel.setAlignment(QtCore.Qt.AlignRight|QtCore.Qt.AlignTrailing|QtCore.Qt.AlignVCenter)
 self.mileageLabel.setObjectName("mileageLabel")
 self.hboxlayout.addWidget(self.mileageLabel)
 self.gridlayout.addLayout(self.hboxlayout, 2, 0, 1, 1)
 self.stackedWidget = QtWidgets.QStackedWidget(VehicleRentalDlg)
 self.stackedWidget.setObjectName("stackedWidget")
 self.page_2 = QtWidgets.QWidget()
 self.page_2.setObjectName("page_2")
 self.gridlayout1 = QtWidgets.QGridLayout(self.page_2)
 self.gridlayout1.setContentsMargins(9, 9, 9, 9)
 self.gridlayout1.setSpacing(6)
 self.gridlayout1.setObjectName("gridlayout1")
 self.colorComboBox = QtWidgets.QComboBox(self.page_2)
 self.colorComboBox.setObjectName("colorComboBox")
 self.colorComboBox.addItem("")
 self.colorComboBox.addItem("")
 self.colorComboBox.addItem("")
 self.colorComboBox.addItem("")
 self.colorComboBox.addItem("")
 self.colorComboBox.addItem("")
 self.colorComboBox.addItem("")
 self.gridlayout1.addWidget(self.colorComboBox, 0, 1, 1, 1)
 self.label_4 = QtWidgets.QLabel(self.page_2)
 self.label_4.setObjectName("label_4")
 self.gridlayout1.addWidget(self.label_4, 0, 0, 1, 1)
 self.label_5 = QtWidgets.QLabel(self.page_2)
 self.label_5.setObjectName("label_5")
 self.gridlayout1.addWidget(self.label_5, 1, 0, 1, 1)
 self.seatsSpinBox = QtWidgets.QSpinBox(self.page_2)
 self.seatsSpinBox.setAlignment(QtCore.Qt.AlignRight)
 self.seatsSpinBox.setMinimum(2)
 self.seatsSpinBox.setMaximum(12)
 self.seatsSpinBox.setProperty("value", 4)
 self.seatsSpinBox.setObjectName("seatsSpinBox")
 self.gridlayout1.addWidget(self.seatsSpinBox, 1, 1, 1, 1)
 self.stackedWidget.addWidget(self.page_2)
 self.page = QtWidgets.QWidget()
 self.page.setObjectName("page")
 self.gridlayout2 = QtWidgets.QGridLayout(self.page)
 self.gridlayout2.setContentsMargins(9, 9, 9, 9)
 self.gridlayout2.setSpacing(6)
 self.gridlayout2.setObjectName("gridlayout2")
 self.weightSpinBox = QtWidgets.QSpinBox(self.page)
 self.weightSpinBox.setAlignment(QtCore.Qt.AlignRight)
 self.weightSpinBox.setMinimum(1)
 self.weightSpinBox.setMaximum(8)
 self.weightSpinBox.setObjectName("weightSpinBox")
 self.gridlayout2.addWidget(self.weightSpinBox, 0, 1, 1, 1)
 self.label_3 = QtWidgets.QLabel(self.page)
 self.label_3.setObjectName("label_3")
 self.gridlayout2.addWidget(self.label_3, 1, 0, 1, 1)
 self.label_2 = QtWidgets.QLabel(self.page)
 self.label_2.setObjectName("label_2")
 self.gridlayout2.addWidget(self.label_2, 0, 0, 1, 1)
 self.volumeSpinBox = QtWidgets.QSpinBox(self.page)
 self.volumeSpinBox.setAlignment(QtCore.Qt.AlignRight)
 self.volumeSpinBox.setMinimum(4)
 self.volumeSpinBox.setMaximum(22)
 self.volumeSpinBox.setProperty("value", 10)
 self.volumeSpinBox.setObjectName("volumeSpinBox")
 self.gridlayout2.addWidget(self.volumeSpinBox, 1, 1, 1, 1)
 self.stackedWidget.addWidget(self.page)
 self.gridlayout.addWidget(self.stackedWidget, 1, 0, 1, 1)
 self.hboxlayout1 = QtWidgets.QHBoxLayout()
 self.hboxlayout1.setContentsMargins(0, 0, 0, 0)
 self.hboxlayout1.setSpacing(6)
 self.hboxlayout1.setObjectName("hboxlayout1")
 self.label = QtWidgets.QLabel(VehicleRentalDlg)
 self.label.setObjectName("label")
 self.hboxlayout1.addWidget(self.label)
 self.vehicleComboBox = QtWidgets.QComboBox(VehicleRentalDlg)
 self.vehicleComboBox.setObjectName("vehicleComboBox")
 self.vehicleComboBox.addItem("")
 self.vehicleComboBox.addItem("")
 self.hboxlayout1.addWidget(self.vehicleComboBox)
 self.gridlayout.addLayout(self.hboxlayout1, 0, 0, 1, 1)
 self.label_4.setBuddy(self.colorComboBox)
 self.label_5.setBuddy(self.seatsSpinBox)
 self.label_3.setBuddy(self.volumeSpinBox)
 self.label_2.setBuddy(self.seatsSpinBox)
 self.label.setBuddy(self.vehicleComboBox)

 self.retranslateUi(VehicleRentalDlg)
 self.stackedWidget.setCurrentIndex(0)
 self.vehicleComboBox.currentIndexChanged['int'].connect(self.stackedWidget.setCurrentIndex)
 self.buttonBox.accepted.connect(VehicleRentalDlg.accept)
 self.buttonBox.rejected.connect(VehicleRentalDlg.reject)
 QtCore.QMetaObject.connectSlotsByName(VehicleRentalDlg)

 def retranslateUi(self, VehicleRentalDlg):
 _translate = QtCore.QCoreApplication.translate
 VehicleRentalDlg.setWindowTitle(_translate("VehicleRentalDlg", "Vehicle Rental"))
 self.label_6.setText(_translate("VehicleRentalDlg", "Max. Mileage:"))
 self.mileageLabel.setText(_translate("VehicleRentalDlg", "1000 miles"))
 self.colorComboBox.setItemText(0, _translate("VehicleRentalDlg", "Black"))
 self.colorComboBox.setItemText(1, _translate("VehicleRentalDlg", "Blue"))
 self.colorComboBox.setItemText(2, _translate("VehicleRentalDlg", "Green"))
 self.colorComboBox.setItemText(3, _translate("VehicleRentalDlg", "Red"))
 self.colorComboBox.setItemText(4, _translate("VehicleRentalDlg", "Silver"))
 self.colorComboBox.setItemText(5, _translate("VehicleRentalDlg", "White"))
 self.colorComboBox.setItemText(6, _translate("VehicleRentalDlg", "Yellow"))
 self.label_4.setText(_translate("VehicleRentalDlg", "Co&lor:"))
 self.label_5.setText(_translate("VehicleRentalDlg", "&Seats:"))
 self.weightSpinBox.setSuffix(_translate("VehicleRentalDlg", " tons"))
 self.label_3.setText(_translate("VehicleRentalDlg", "Volu&me:"))
 self.label_2.setText(_translate("VehicleRentalDlg", "&Weight:"))
 self.volumeSpinBox.setSuffix(_translate("VehicleRentalDlg", " cu m"))
 self.label.setText(_translate("VehicleRentalDlg", "&Vehicle Type:"))
 self.vehicleComboBox.setItemText(0, _translate("VehicleRentalDlg", "Car"))
 self.vehicleComboBox.setItemText(1, _translate("VehicleRentalDlg", "Van"))

/home/yrd/eric_workspace/Vehicle/vehiclerentaldlg.py

# -*- coding: utf-8 -*-

"""
Module implementing VehicleRentalDlg.
"""
import sys
from PyQt5.QtCore import pyqtSlot
from PyQt5.QtWidgets import QDialog,QApplication

from Ui_vehiclerentaldlg import Ui_VehicleRentalDlg


class VehicleRentalDlg(QDialog, Ui_VehicleRentalDlg):
 """
 Class documentation goes here.
 """
 def __init__(self, parent=None):
 """
 Constructor

 @param parent reference to the parent widget
 @type QWidget
 """
 super(VehicleRentalDlg, self).__init__(parent)
 self.setupUi(self)
 self.vehicleComboBox.setFocus()

 @pyqtSlot(int)
 def on_weightSpinBox_valueChanged(self, amount):
 self.mileageLabel.setText("{0} miles".format(8000 / amount))


 @pyqtSlot(str)
 def on_vehicleComboBox_currentIndexChanged(self, text):
 if text == "Car":
 self.mileageLabel.setText("1000 miles")
 else:
 self.on_weightSpinBox_valueChanged(
 self.weightSpinBox.value()) 

if __name__ == "__main__":
 app = QApplication(sys.argv)
 form = VehicleRentalDlg() 
 form.show()
 app.exec_()

运行结果：