from PyQt5 import QtCore, QtGui, QtWidgets
from ui_mainwindow import Ui_MainWindow
class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
  def __init__(self, parent=None):
    super(MainWindow, self).__init__(parent)
    self.setupUi(self)

    self.Title.setText("hello Python")
    self.World.clicked.connect(self.onWorldClicked)
    self.China.clicked.connect(self.onChinaClicked)
    self.lineEdit.textChanged.connect(self.onlineEditTextChanged)

  def onWorldClicked(self, remark):
    print(remark)
    self.Title.setText("Hello World")

  def onChinaClicked(self):
    self.Title.setText("Hello China")

  def onlineEditTextChanged(self,p_str):
    self.Title.setText(p_str)

from PyQt5 import QtCore, QtGui, QtWidgets
from mainwindow import MainWindow
import sys

if __name__ == "__main__":
  app = QtWidgets.QApplication(sys.argv)
  mainWindow = MainWindow()
  mainWindow.show()
  sys.exit(app.exec_())