from PyQt5 import QtCore, QtGui, QtWidgets

class Helper(QtCore.QObject):
    def __init__(self, parent=None):
        super(Helper, self).__init__(parent)
        self.m_widgets = []

    def appendWidget(self, widget):
        self.m_widgets.append(widget)
        widget.installEventFilter(self)

    def eventFilter(self, obj, event):
        if obj in self.m_widgets and event.type() == QtCore.QEvent.KeyPress:
            if event.key() == QtCore.Qt.Key_Tab:
                # create new event
                new_event = QtGui.QKeyEvent(QtCore.QEvent.KeyPress, 
                    QtCore.Qt.Key_Down, 
                    QtCore.Qt.NoModifier)
                # send new event
                QtCore.QCoreApplication.postEvent(obj, new_event)
                # if True, the event is discarded
                return True
        return super(Helper, self).eventFilter(obj, event)


class Widget(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(Widget, self).__init__(parent)
        self.table = QtWidgets.QTableWidget(4, 4)
        lay = QtWidgets.QVBoxLayout(self)
        lay.addWidget(self.table)

        helper = Helper(self)
        helper.appendWidget(self.table)


if __name__ == '__main__':
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec_())