test.py

from PySide2 import QtWidgets, QtGui, QtCore

class PublishTable(QtWidgets.QTableWidget):
    def paintEvent(self, event):
        super(PublishTable, self).paintEvent(event)
        painter = QtGui.QPainter(self)
        gradient = QtGui.QLinearGradient(QtCore.QPoint(0,0), QtCore.QPoint(self.width()/2, 0))      
        painter.setBrush(QtGui.QBrush(gradient))
        #painter.setPen(QtCore.Qt.transparent)        
        rect = QtCore.QRect(0,
                            0,
                            self.width()*.5,
                            self.height())
        painter.drawRect(rect)

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