Не получается послать сигнал в другой класс

У меня есть три окна:

• первое - главное окно приложения,
• второе окно приложения, и
• третье окно, которое находится в отдельном классе.

В каждом из них есть по кнопке: кнопка в главном окне открывает мини окно, которое в отдельном классе, поверх основного окна.

Кнопка, которая находится в мини окне, должна закрыть мини окно и запустить второе окно приложения.

Решил использовать pyqtSignal для решения этой задачи, но выскакивает следующая ошибка:

Traceback (most recent call last):
  File "d:/Python/test/main.py", line 55, in <module>
    application = App()
  File "d:/Python/test/main.py", line 29, in __init__
    self.init_UI()
  File "d:/Python/test/main.py", line 38, in init_UI
    self.mysignal.connect(self.second_UI)
AttributeError: 'PyQt5.QtCore.pyqtSignal' object has no attribute 'connect'

Надеюсь на вашу помощь!

main.py

import sys

from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QWidget

import main_ui
import mini_ui
import second_ui


class Mini_UI(QWidget):
    def __init__(self):
        super(Mini_UI, self).__init__()
        self.init_UI()

    def init_UI(self):
        self.mini_ui = mini_ui.Ui_Form()
        self.mini_ui.setupUi(self)
        self.mini_ui.pushButton.clicked.connect(self.close)
        self.mini_ui.pushButton.clicked.connect(self.show_second_ui)

    def show_second_ui(self):
        App().mysignal.emit()                                  ######


class App(QtWidgets.QMainWindow):
    def __init__(self):
        super(App, self).__init__()
        self.init_UI()


    def init_UI(self):
        self.main_ui = main_ui.Ui_MainWindow()
        self.main_ui.setupUi(self)
        self.main_ui.pushButton.clicked.connect(self.show_mini_ui)

        self.mysignal = QtCore.pyqtSignal()                   ######
        self.mysignal.connect(self.second_UI)                 ######

    def second_UI(self):
        self.second_ui = second_ui.Ui_MainWindow()
        self.second_ui.setupUi(self)
        self.second_ui.pushButton.clicked.connect(self.init_UI)

    def show_mini_ui(self):
        self.mini_window = Mini_UI()
        self.mini_window.show()



if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    application = App()
    application.show()

    sys.exit(app.exec())

main_ui.py

from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(210, 50, 351, 131))
        font = QtGui.QFont()
        font.setPointSize(26)
        self.label.setFont(font)
        self.label.setAlignment(QtCore.Qt.AlignCenter)
        self.label.setObjectName("label")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(240, 230, 291, 111))
        self.pushButton.setObjectName("pushButton")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 21))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

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

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setText(_translate("MainWindow", "ПЕРВОЕ ОКНО"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))

second_ui.py

from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(800, 600)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(210, 50, 351, 131))
        font = QtGui.QFont()
        font.setPointSize(26)
        self.label.setFont(font)
        self.label.setAlignment(QtCore.Qt.AlignCenter)
        self.label.setObjectName("label")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(240, 230, 291, 111))
        self.pushButton.setObjectName("pushButton")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 800, 21))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

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

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setText(_translate("MainWindow", "ВТОРОЕ ОКНО"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))

mini_ui.py

from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_Form(object):
    def setupUi(self, Form):
        Form.setObjectName("Form")
        Form.resize(400, 300)
        self.pushButton = QtWidgets.QPushButton(Form)
        self.pushButton.setGeometry(QtCore.QRect(120, 100, 131, 71))
        self.pushButton.setObjectName("pushButton")

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

    def retranslateUi(self, Form):
        _translate = QtCore.QCoreApplication.translate
        Form.setWindowTitle(_translate("Form", "Form"))
        self.pushButton.setText(_translate("Form", "PushButton"))