import sys
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *


class DialogDemo(QMainWindow):

def __init__(self, parent=None):
super(DialogDemo, self).__init__(parent)
self.setWindowTitle("Dialog 例子")
self.resize(350, 300)

self.btn = QPushButton(self)
self.btn.setText("弹出对话框")
self.btn.move(50, 50)
self.btn.clicked.connect(self.showdialog)

def showdialog(self):
dialog = QDialog()
btn = QPushButton("ok", dialog)
btn.move(50, 50)
dialog.setWindowTitle("Dialog")
dialog.setWindowModality(Qt.ApplicationModal)
dialog.exec_()


if __name__ == '__main__':
app = QApplication(sys.argv)
demo = DialogDemo()
demo.show()
sys.exit(app.exec_())