Code removed from the question
The error happens because you haven't set any cell widgets, and so
cellWidget() will always return
None. However, this is irrelevant, since you actually need to query the checked-state of the table-widget items (which is what you have made checkable).
Your code should probably look more like this:
def ButtonClicked(self): checked_listV5 =  for i in range(self.tableV5.rowCount()): if self.tableV5.item(i, 0).checkState() == QtCore.Qt.Checked: checked_listV5.append(self.tableV5.item(i, 1).text())