How to connect 2 windows using pyqtSignal in PyQt?

Question

I create simple application using 2 windows, and i want connect it with button using pyqtsignal, but when i run the application display information "TypeError: pyqtSignal must be bound to a QObject, not 'Form1'":

from PyQt4 import QtCore, QtGui
import form2
import sys
from functools import partial
from PyQt4.QtCore import pyqtSignal
from lib2to3.fixer_util import String

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Form1(QtGui.QMainWindow):
    Form2Signal = pyqtSignal(str, str)

    def __init__(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(319, 147)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.bt_form1 = QtGui.QPushButton(self.centralwidget)
        self.bt_form1.setGeometry(QtCore.QRect(110, 30, 101, 41))
        self.bt_form1.setObjectName(_fromUtf8("bt_form1"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 319, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)

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

    def retranslateUi(self, MainWindow):
        self.bt_form1.clicked.connect(self.Form2Signal.emit(String))
        MainWindow.setWindowTitle(_translate("MainWindow", "Form_1", None))
        self.bt_form1.setText(_translate("MainWindow", "FORM_1", None))

class Form2(QtGui.QMainWindow):
    Form1Signal = pyqtSignal(str, str)

    def __init__(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(319, 147)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.bt_form2 = QtGui.QPushButton(self.centralwidget)
        self.bt_form2.setGeometry(QtCore.QRect(110, 30, 101, 41))
        self.bt_form2.setObjectName(_fromUtf8("bt_form2"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 319, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)

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

    def retranslateUi(self, MainWindow):
        self.bt_form2.clicked.connect(self.Form1Signal.emit)
        MainWindow.setWindowTitle(_translate("MainWindow", "Form_2", None))
        self.bt_form2.setText(_translate("MainWindow", "FORM_2", None))

class MainWidget(QtGui.QMainWindow):
    def __init__(self, parent=None):
        super(MainWidget, self).__init__(parent)
        self.stack = QtGui.QStackedWidget()
        layout = QtGui.QVBoxLayout(self)
        layout.addWidget(self.stack)
        self.form1 = Form1(self)
        self.form2 = Form2(self)
        self.stack.addWidget(self.form1)
        self.stack.addWidget(self.form2)
        self.form1.Form2Signal.connect(partial(self.stack.setCurrentWidget,self.form2))
        self.form2.Form1Signal.connect(partial(self.stack.setCurrentWidget,self.form1))
        self.stack.setCurrentWidget(self.form1)

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    w = MainWidget()
    w.show()
    app.exec_()
    sys.exit()

Answer 1

Add super(Form1, self).__init__() in __init__ method of Form1 class. Do the same for Form2