class OwnHistogram(QgsHistogramDiagram):
    def __init__(self):
        super(OwnHistogram, self).__init__()

    def renderDiagram(self, feature, renderContext, diagramSettings, position):
        # Here I want to see if function is entered:
        print('Try to override')
        super(OwnHistogram, self).renderDiagram(
            feature, renderContext, diagramSettings, position)

def clone(self):
    return OwnHistogram()