QTableWidgetTest.py

from PyQt5.QtGui import * 
from PyQt5.QtCore import * 
from PyQt5.QtWidgets import * 
import sys

class Widget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setLayout(QVBoxLayout())
        self.le =  QLineEdit(":P", self)
        self.le.setPlaceholderText("Value to be changed")
        self.combo = QComboBox(self)
        btn =  QPushButton("Press Me to Change", self)
        btn.clicked.connect(self.onClicked)
        self.table = QTableWidget(self)

        self.layout().addWidget(self.le)
        self.layout().addWidget(self.combo)
        self.layout().addWidget(btn)
        self.layout().addWidget(self.table)

        self.table.setRowCount(4)
        self.table.setColumnCount(2)

        for i in range(self.table.rowCount()):
            for j in range(self.table.columnCount()):
                self.table.setItem(i, j, QTableWidgetItem("Item ({},{})".format(i, j)))

        self.combo.addItems(["{}, {}".format(i, j) for i in range(self.table.rowCount()) for j in range(self.table.columnCount())])

    def onClicked(self):
        x, y =  self.combo.currentText().split(",")
        self.table.item(int(x), int(y)).setText(self.le.text())

def main():  
    app 	= QApplication(sys.argv)

    widget =  Widget()
    widget.show()
    return app.exec_()
 
if __name__ == '__main__':
    main()