def evalDrop(ctx, u):
    if ctx.dataset.store.graph_aware:
        for g in _graphAll(ctx, u.graphiri):
            ctx.dataset.store.remove_graph(g)
    else:
        evalClear(ctx, u)
http://www.w3.org/TR/sparql11-update/#drop
dataset/ETHPy150Open RDFLib/rdflib/rdflib/plugins/sparql/update.py/evalDrop