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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def remove_isolated_nodes_op(graph):
 """Build a new graph excluding the isolated nodes. :param pybel.BELGraph graph: A BEL graph :rtype: pybel.BELGraph """

    rv = graph.copy()
    nodes = list(nx.isolates(rv))
    rv.remove_nodes_from(nodes)
    return rv