PyQt5 Qtablewidget and connecting to buttons

I have created a Qtablewidget as a class, and add_button to add rows, a delete_button to remove rows from table down upwards. I would like to connect functions to buttons, but it doesn't work correctly. I have used getattr method to call the function, still does not work.

The table

to explain more, those scriptlines are giving attributte errors. when they are called by button.clicked.connect method.

add_button.clicked.connect(self._addrow)
delete_button.clicked.connect(self._removeItem)

The script is as below:

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


class loadtable(QtWidgets.QTableWidget):
    def __init__(self, parent=None):
        super(loadtable, self).__init__(parent)

        self.setColumnCount(5)
        self.setRowCount(1)
        self.setFont(QtGui.QFont("Helvetica", 10, QtGui.QFont.Normal, italic=False))   
        headertitle = ("A","B","C","D","E")
        self.setHorizontalHeaderLabels(headertitle)
        self.verticalHeader().setVisible(False)
        self.horizontalHeader().setHighlightSections(False)
        self.horizontalHeader().setSectionResizeMode(QtWidgets.QHeaderView.Fixed)
        self.setSelectionMode(QtWidgets.QAbstractItemView.NoSelection)
        self.setColumnWidth(0, 130)
        combox_lay = QtWidgets.QComboBox(self)
        combox_lay.addItems(["I","II"])
        self.setCellWidget(0, 4, combox_lay)


        self.cellChanged.connect(self._cellclicked)
        #self.cellChanged.connect(self._addrow)
        #self.cellDoubleClicked.connect(self._removerow)

    def _cellclicked(self):
        self.value = self.currentItem()
        self.value.setTextAlignment(Qt.AlignCenter)
        #if self.value is not None:
           #return self.value.setTextAlignment(Qt.AlignCenter)        

    def _addrow(self):
        rowcount = self.rowCount()
        print(rowcount)
        self.setRowCount(rowcount+1)
        combox_add = QtWidgets.QComboBox(self)
        combox_add.addItems(["I","II"])
        self.setCellWidget(rowcount, 4, combox_add)

    def _removerow(self):
        self.removeRow(1)


class thirdtabloads(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(thirdtabloads, self).__init__(parent)      
        table = loadtable()


        button_layout = QtWidgets.QVBoxLayout()
        add_button = QtWidgets.QPushButton("Add")
        add_button.clicked.connect(self._addrow)
        delete_button = QtWidgets.QPushButton("Delete")
        delete_button.clicked.connect(self._removeItem)
        button_layout.addWidget(add_button, alignment=QtCore.Qt.AlignBottom)
        button_layout.addWidget(delete_button, alignment=QtCore.Qt.AlignTop)


        tablehbox = QtWidgets.QHBoxLayout()
        tablehbox.setContentsMargins(10,10,10,10)
        tablehbox.addWidget(table)

        grid = QtWidgets.QGridLayout(self)
        grid.addLayout(button_layout, 0, 1)
        grid.addLayout(tablehbox, 0, 0)        



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

To add a row you must use insertRow(), to remove the last row use removeRow() and pass the last row and remember that the numbering starts from 0 so the last row is self.rowCount() - 1.

On the other hand, your connection is incorrect, I ask you: Who owns the slot _addrow() and _removerow()? belongs to LoadTable, so to access them we need an object of that class, ie table._addrow and table._removerow.

import sys
from PyQt5 import QtCore, QtGui, QtWidgets


class LoadTable(QtWidgets.QTableWidget):
    def __init__(self, parent=None):
        super(LoadTable, self).__init__(1, 5, parent)
        self.setFont(QtGui.QFont("Helvetica", 10, QtGui.QFont.Normal, italic=False))   
        headertitle = ("A","B","C","D","E")
        self.setHorizontalHeaderLabels(headertitle)
        self.verticalHeader().hide()
        self.horizontalHeader().setHighlightSections(False)
        self.horizontalHeader().setSectionResizeMode(QtWidgets.QHeaderView.Fixed)

        self.setSelectionMode(QtWidgets.QAbstractItemView.NoSelection)
        self.setColumnWidth(0, 130)

        combox_lay = QtWidgets.QComboBox(self)
        combox_lay.addItems(["I","II"])
        self.setCellWidget(0, 4, combox_lay)

        self.cellChanged.connect(self._cellclicked)

    @QtCore.pyqtSlot(int, int)
    def _cellclicked(self, r, c):
        it = self.item(r, c)
        it.setTextAlignment(QtCore.Qt.AlignCenter)        

    @QtCore.pyqtSlot()
    def _addrow(self):
        rowcount = self.rowCount()
        self.insertRow(rowcount)
        combox_add = QtWidgets.QComboBox(self)
        combox_add.addItems(["I","II"])
        self.setCellWidget(rowcount, 4, combox_add)

    @QtCore.pyqtSlot()
    def _removerow(self):
        if self.rowCount() > 0:
            self.removeRow(self.rowCount()-1)


class ThirdTabLoads(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(ThirdTabLoads, self).__init__(parent)    

        table = LoadTable()

        add_button = QtWidgets.QPushButton("Add")
        add_button.clicked.connect(table._addrow)

        delete_button = QtWidgets.QPushButton("Delete")
        delete_button.clicked.connect(table._removerow)

        button_layout = QtWidgets.QVBoxLayout()
        button_layout.addWidget(add_button, alignment=QtCore.Qt.AlignBottom)
        button_layout.addWidget(delete_button, alignment=QtCore.Qt.AlignTop)


        tablehbox = QtWidgets.QHBoxLayout()
        tablehbox.setContentsMargins(10, 10, 10, 10)
        tablehbox.addWidget(table)

        grid = QtWidgets.QGridLayout(self)
        grid.addLayout(button_layout, 0, 1)
        grid.addLayout(tablehbox, 0, 0)        


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