Error from QTableView selectionChanged

If I try to get the signal when my tableview changes, Python raises this error:

Traceback (most recent call last):
  File "UIreadresultwindow.py", line 361, in <module>
    ui.setupUi(ReadResultWindow)
  File "UIreadresultwindow.py", line 113, in setupUi
    self.tableEntity.selectionModel().selectionChanged.connect(self.change
_display_result)
AttributeError: 'NoneType' object has no attribute 'selectionChanged'

I define tableEntity as:

self.tableEntity = QtWidgets.QTableView(self.centralWidget)

Edit: At first my QTableView is empty. I have to open a file to fill it.

Edit2: To be more specific, I have something like this:

from PyQt5 import QtCore, QtGui, QtWidgets
class Ui_ReadResultWindow(object):
    def setupUi(self, ReadResultWindow):
        ReadResultWindow.setObjectName("ReadResultWindow")
        ReadResultWindow.resize(661, 438)
        self.centralWidget = QtWidgets.QWidget(ReadResultWindow)
        self.centralWidget.setObjectName("centralWidget")
        self.tableEntity = QtWidgets.QTableView(self.centralWidget)
        self.tableEntity.setObjectName("tableEntity")
        self.Open = QtWidgets.QPushButton(self.centralWidget)
        self.Open.setObjectName("Open")

        self.Open.clicked.connect(self.on_open_file)
        self.tableEntity.selectionModel().selectionChanged.connect(self.change_display_result)


    def on_open_file(self):
        x=[1,2,3,4]
        self.model= QtGui.QStandardItemModel()
        for item in x:
            self.model.invisibleRootItem().appendRow(
                QtGui.QStandardItem(str(x)))

        self.proxy= QtCore.QSortFilterProxyModel()
        self.proxy.setSourceModel(self.model)
        self.tableEntity.setModel(self.proxy)
        self.tableEntity.resizeColumnsToContents()

    def change_display_result(self,selected,deselected):
        index_entity   =  self.tableEntity.selectionModel().selectedIndexes()
        temp_entity    =  self.tableEntity.selectionModel().model()
        for index in sorted(index_entity):
            print(str(temp_entity.data(index)))

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    ReadResultWindow = QtWidgets.QMainWindow()
    ui = Ui_ReadResultWindow()
    ui.setupUi(ReadResultWindow)
    ReadResultWindow.show()
    sys.exit(app.exec_())

The reason why you get that error is that you did not set the model on the table before trying to access the selection-model. The best way to fix this is to move the model setup code out of on_open_file and into setupUi. The on_open_file then just needs to clear the model before reloading the data.

Below is a re-write of your example. Note that I had to fix quite a few other things to get it to work (mainly the central-widget and layout).

import sys, random
from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_ReadResultWindow(object):
    def setupUi(self, ReadResultWindow):
        ReadResultWindow.resize(661, 438)

        self.tableEntity = QtWidgets.QTableView()

        self.model = QtGui.QStandardItemModel()
        self.proxy = QtCore.QSortFilterProxyModel()
        self.proxy.setSourceModel(self.model)
        self.tableEntity.setModel(self.proxy)
        self.tableEntity.selectionModel().selectionChanged.connect(
            self.change_display_result)

        self.Open = QtWidgets.QPushButton('Test')
        self.Open.clicked.connect(self.on_open_file)

        widget = QtWidgets.QWidget(ReadResultWindow)
        layout = QtWidgets.QVBoxLayout(widget)
        layout.addWidget(self.tableEntity)
        layout.addWidget(self.Open)

        ReadResultWindow.setCentralWidget(widget)

    def on_open_file(self):
        self.model.setRowCount(0)
        x = random.sample(range(10, 100), 10)
        for item in x:
            self.model.invisibleRootItem().appendRow(
                QtGui.QStandardItem(str(item)))
        self.tableEntity.resizeColumnsToContents()

    def change_display_result(self,selected,deselected):
        index_entity = self.tableEntity.selectionModel().selectedIndexes()
        temp_entity = self.tableEntity.selectionModel().model()
        for index in sorted(index_entity):
            print(str(temp_entity.data(index)))

if __name__ == "__main__":

    app = QtWidgets.QApplication(sys.argv)
    ReadResultWindow = QtWidgets.QMainWindow()
    ui = Ui_ReadResultWindow()
    ui.setupUi(ReadResultWindow)
    ReadResultWindow.show()
    sys.exit(app.exec_())