Pyqt5设置返回键和跳转键

import sys
from 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_())