how to connect two windows in pyqt4?

Question

from PyQt4 import QtCore, QtGui

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 Ui_Dialog(object):
    def setupUi(self, Dialog):
        Dialog.setObjectName(_fromUtf8("Dialog"))
        Dialog.resize(833, 592)
        self.label = QtGui.QLabel(Dialog)
        self.label.setGeometry(QtCore.QRect(5, 9, 1366, 700))
        self.label.setText(_fromUtf8(""))
        self.label.setPixmap(QtGui.QPixmap(_fromUtf8("H:/Community/images/Library-Books2.jpg")))
        self.label.setScaledContents(True)
        self.label.setObjectName(_fromUtf8("label"))
        self.label_2 = QtGui.QLabel(Dialog)
        self.label_2.setGeometry(QtCore.QRect(40, 90, 91, 31))
        font = QtGui.QFont()
        font.setFamily(_fromUtf8("Plantagenet Cherokee"))
        font.setPointSize(14)
        font.setBold(True)
        font.setWeight(75)
        self.label_2.setFont(font)
        self.label_2.setObjectName(_fromUtf8("label_2"))
        self.lineEdit = QtGui.QLineEdit(Dialog)
        self.lineEdit.setGeometry(QtCore.QRect(160, 90, 361, 31))
        font = QtGui.QFont()
        font.setFamily(_fromUtf8("Arial"))
        font.setPointSize(9)
        self.lineEdit.setFont(font)
        self.lineEdit.setObjectName(_fromUtf8("lineEdit"))
        self.pushButton = QtGui.QPushButton(Dialog)
        self.pushButton.setGeometry(QtCore.QRect(540, 92, 51, 31))
        self.pushButton.setText(_fromUtf8(""))
        icon = QtGui.QIcon()
        icon.addPixmap(QtGui.QPixmap(_fromUtf8("H:/Community/community/Library/build/classes/library/search.png")), QtGui.QIcon.Normal, QtGui.QIcon.Off)
        self.pushButton.setIcon(icon)
        self.pushButton.setFlat(False)
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        self.plainTextEdit = QtGui.QPlainTextEdit(Dialog)
        self.plainTextEdit.setGeometry(QtCore.QRect(10, 140, 900, 391))
        self.plainTextEdit.setBackgroundVisible(False)
        self.plainTextEdit.setCenterOnScroll(False)
        self.plainTextEdit.setObjectName(_fromUtf8("plainTextEdit"))
        self.pushButton_2 = QtGui.QPushButton(Dialog)
        self.pushButton_2.setGeometry(QtCore.QRect(410, 540, 90, 50))
        self.pushButton_2.setText(_fromUtf8(""))
        self.connect(self.pushButton, QtCore.SIGNAL('clicked()'), self.open)
        icon1 = QtGui.QIcon()
        icon1.addPixmap(QtGui.QPixmap(_fromUtf8("H:/Community/images/new-button3 - Copy.png")), QtGui.QIcon.Normal, QtGui.QIcon.Off)
        self.pushButton_2.setIcon(icon1)
        self.pushButton_2.setIconSize(QtCore.QSize(80, 80))
        self.pushButton_2.setFlat(True)
        self.pushButton_2.setObjectName(_fromUtf8("pushButton_2"))

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

    def open(self):

        fileName = QtGui.QFileDialog.getOpenFileName(self, 'OpenFile')
        self.LineEdit.setText(fileName)
        print(fileName)

    def retranslateUi(self, Dialog):
        Dialog.setWindowTitle(_translate("Dialog", "Dialog", None))
        self.label_2.setText(_translate("Dialog", "FileName", None))

Answer 1

Generally when I have windows working together I will set one as the others parent or have methods for one that receives data from the other. For example:

class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        self.setupUi(self)
        self.run_btn.clicked.connect(self.setup_project)

    def setup_project(self):
        self.project = ProjectParams(parent=self)
        self.project.show()
        if self.project.exec_() == QtWidgets.QDialog.Accepted:
            self.params = self.project.params
            self.loops = self.project.loops

class ProjectParams(QtWidgets.QDialog, Ui_ProjectParams):
    def __init__(self, parent=None):
        QtWidgets.QDialog.__init__(self, parent=parent)
        self.setupUi(self)
        self.buttonBox.button(QtWidgets.QDialogButtonBox.Ok).setEnabled(False)
        self.params = {}

From your error I would think you need to change:

self.connect(self.pushButton, QtCore.SIGNAL('clicked()'), self.open)

to:

self.pushButton.clicked.connect(self.open)