pyqt5 关于主窗口闪退

from PyQt5.QtWidgets import *
import sys


class Main(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("主窗口")
        button = QPushButton("弹出子窗口", self)
        button.clicked.connect(self.show_child)  # 关联子窗口调用函数

    def show_child(self):
        child_window = Child()
        child_window.show()

class Child(QDialog):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("子窗口")

if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = Main()
    window.show()
    sys.exit(app.exec_())

def show_child(self):
        self.child_window = Child()
        self.child_window.show()