PyQt5 - closes application bec. of error with .value() method

whenever I click a button in the second window of my PyQt5 application that should just print the value of a QDateEdit in the GUI, it closes with the line: "Process finished with exit code -1073740791 (0xC0000409)". I figured out that the problem has something to do with the .value() method. Here's the Minimal to reproduce the bug with the Ui_Form class below:

import sys
from PyQt5 import QtWidgets
from ui.fenster import Ui_Form


app = QtWidgets.QApplication(sys.argv)

class AppendWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.ui = Ui_Form()
        self.ui.setupUi(self)
        self.ui.submit.clicked.connect(self.show_value)


    def show_value(self):
        print(self.ui.date.value())






append = AppendWindow()

append.show()
sys.exit(app.exec_())

Ui_Form:

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName("Form")
        Form.resize(413, 215)
        self.date = QtWidgets.QDateEdit(Form)
        self.date.setGeometry(QtCore.QRect(72, 26, 321, 20))
        self.date.setObjectName("date")
        self.label = QtWidgets.QLabel(Form)
        self.label.setGeometry(QtCore.QRect(9, 26, 57, 16))
        self.label.setObjectName("label")
        self.age = QtWidgets.QSpinBox(Form)
        self.age.setGeometry(QtCore.QRect(70, 120, 321, 20))
        self.age.setObjectName("age")
        self.label_2 = QtWidgets.QLabel(Form)
        self.label_2.setGeometry(QtCore.QRect(10, 120, 23, 16))
        self.label_2.setObjectName("label_2")
        self.label_3 = QtWidgets.QLabel(Form)
        self.label_3.setGeometry(QtCore.QRect(9, 69, 27, 16))
        self.label_3.setObjectName("label_3")
        self.name = QtWidgets.QPlainTextEdit(Form)
        self.name.setGeometry(QtCore.QRect(72, 69, 319, 21))
        self.name.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.name.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.name.setObjectName("name")
        self.submit = QtWidgets.QPushButton(Form)
        self.submit.setGeometry(QtCore.QRect(170, 170, 75, 23))
        self.submit.setObjectName("submit")

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        _translate = QtCore.QCoreApplication.translate
        Form.setWindowTitle(_translate("Form", "Form"))
        self.label.setText(_translate("Form", "Geburtsjahr"))
        self.label_2.setText(_translate("Form", "Alter"))
        self.label_3.setText(_translate("Form", "Name"))
        self.submit.setText(_translate("Form", "Absenden!"))

Does anyone know how to fix this? I appreciate your help!

You need to add app.exec() in your main code in order to start the main loop.

app = QtWidgets.QApplication(sys.argv)
app.exec()

The main loop handles all the incoming events and passes them to your GUI elements.