def evalCopy(ctx, u):

    src, dst = u.graph

    srcg = _graphOrDefault(ctx, src)
    dstg = _graphOrDefault(ctx, dst)

    if srcg.identifier == dstg.identifier:
        return

    dstg.remove((None, None, None))

    dstg += srcg
remove all triples from dst
dataset/ETHPy150Open RDFLib/rdflib/rdflib/plugins/sparql/update.py/evalCopy