import sysfrom PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication    class First(QMainWindow):    def __init__(self):    super().__init__()      self.initUI()    def initUI(self):    self.btn = QPushButton("进入页面2", self)    self.btn.move(30, 50)             self.setGeometry(300, 200, 500, 500)    self.setWindowTitle('页面1')   class Second(QMainWindow):  def __init__(self):    super().__init__()      self.initUI()    def initUI(self):    self.btn = QPushButton("进入页面3", self)    self.btn.move(30, 50)    self.setGeometry(300, 200, 290, 150)    self.setWindowTitle('页面2')  class Third(QMainWindow):  def __init__(self):    super().__init__()      self.initUI()    def initUI(self):    self.btn = QPushButton("返回页面1", self)    self.btn.move(30, 50)     self.btn2 = QPushButton("功能函数", self)    self.btn2.move(30, 90)     self.setGeometry(500, 200, 290, 350)    self.setWindowTitle('页面3')    self.btn2.clicked.connect(self.action)  def action(self):    print("这是功能函数")       if __name__ == '__main__':  app = QApplication(sys.argv)  a = First()  b = Second()  c = Third()  a.show()  a.btn.clicked.connect(b.show)  a.btn.clicked.connect(a.close)  b.btn.clicked.connect(c.show)  b.btn.clicked.connect(b.close)  c.btn.clicked.connect(a.show)  c.btn.clicked.connect(c.close)  sys.exit(app.exec_())

from PyQt5 import QtCore, QtGui, QtWidgetsimport sysfrom PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QLabel,/                     QPushButton, QLineEdit, QMenuBar, QStatusBarfrom PyQt5.QtCore import * class FirstWindow(QWidget):   def __init__(self, parent=None):    # super这个用法是调用父类的构造函数    # parent=None表示默认没有父Widget，如果指定父亲Widget，则调用之    super(FirstWindow, self).__init__(parent)    self.setGeometry(500, 500, 500, 500)    self.setWindowTitle('显示')    self.btn = QPushButton(self)    self.btn.setText('进入页面2')    self.btn.move(150, 50)  #下面的一部分是Qtdesigner的代码 class Ui_MainWindow(object):  def setupUi(self, MainWindow):    MainWindow.setObjectName("MainWindow")    MainWindow.resize(624, 479)    self.centralwidget = QtWidgets.QWidget(MainWindow)    self.centralwidget.setObjectName("centralwidget")    self.label = QtWidgets.QLabel(self.centralwidget)    self.label.setGeometry(QtCore.QRect(190, 130, 51, 31))    self.label.setObjectName("label")    self.pushButton = QtWidgets.QPushButton(self.centralwidget)    self.pushButton.setGeometry(QtCore.QRect(330, 260, 75, 23))    self.pushButton.setObjectName("pushButton")    self.lineEdit = QtWidgets.QLineEdit(self.centralwidget)    self.lineEdit.setGeometry(QtCore.QRect(280, 130, 151, 21))    self.lineEdit.setObjectName("lineEdit")    self.label_2 = QtWidgets.QLabel(self.centralwidget)    self.label_2.setGeometry(QtCore.QRect(190, 180, 51, 31))    self.label_2.setObjectName("label_2")    self.lineEdit_2 = QtWidgets.QLineEdit(self.centralwidget)    self.lineEdit_2.setGeometry(QtCore.QRect(280, 190, 151, 21))    self.lineEdit_2.setObjectName("lineEdit_2")    self.pushButton_2 = QtWidgets.QPushButton(self.centralwidget)    self.pushButton_2.setGeometry(QtCore.QRect(200, 260, 75, 23))    self.pushButton_2.setObjectName("pushButton_2")    MainWindow.setCentralWidget(self.centralwidget)    self.menubar = QtWidgets.QMenuBar(MainWindow)    self.menubar.setGeometry(QtCore.QRect(0, 0, 624, 23))    self.menubar.setObjectName("menubar")    MainWindow.setMenuBar(self.menubar)    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.label.setText(_translate("MainWindow", "  长"))    self.pushButton.setText(_translate("MainWindow", "返回"))    self.label_2.setText(_translate("MainWindow", "  宽"))    self.pushButton_2.setText(_translate("MainWindow", "确定")) if __name__ == "__main__":  app = QApplication(sys.argv)  MainWindow = QMainWindow()  ui = Ui_MainWindow()  ui.setupUi(MainWindow)  ex = FirstWindow()  ex.btn.clicked.connect(MainWindow.show)  ex.btn.clicked.connect(ex.close)  ui.pushButton.clicked.connect(ex.show)  ui.pushButton.clicked.connect(MainWindow.close)  ex.show()  sys.exit(app.exec_())