https://stackoverflow.com/questions/53824091

main.py

import sys
from PyQt5 import QtCore, QtGui, QtWidgets

def copy_widget(w):
    if isinstance(w, QtWidgets.QWidget):
        new_w = type(w)()
        if isinstance(w, QtWidgets.QComboBox):
            vals = [w.itemText(ix) for ix in range(w.count())]
            new_w.addItems(vals)
        return new_w

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)

    @QtCore.pyqtSlot()
    def _copyrow(self):
        r = self.currentRow()
        if 0 <= r < self.rowCount():
            cells = {"items": [], "widgets": []}
            for i in range(self.columnCount()):
                it = self.item(r, i)
                if it:
                    cells["items"].append((i, it.clone()))
                w = self.cellWidget(r, i)
                if w:
                    cells["widgets"].append((i, copy_widget(w)))
            self.copy(cells, r+1)

    def copy(self, cells, r):
        self.insertRow(r)
        for i, it in cells["items"]:
            self.setItem(r, i, it)
        for i, w in cells["widgets"]:
            self.setCellWidget(r, i, w)

class FloatDelegate(QtWidgets.QStyledItemDelegate):
    def createEditor(self, parent, option, index):
        editor = QtWidgets.QDoubleSpinBox(parent) 
        editor.setDecimals(5)
        editor.setMinimum(-sys.float_info.max)
        editor.setMaximum(sys.float_info.max)
        return editor

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)

        copy_button = QtWidgets.QPushButton("Copy")
        copy_button.clicked.connect(table._copyrow)

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

        for i in (1, 2, 3):
            delegate = FloatDelegate(self)
            table.setItemDelegateForColumn(i, delegate)    


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