Function takes a subject and an existing graph, returns a new graph with
    all predicate and objects of the existing graph copied to the new_graph with
    subject as the new subject

    Args:
        subject(rdflib.URIRef): A URIRef subject
        existing_graph(rdflib.Graph): A rdflib.Graph

    Returns:
        rdflib.Graph

def copy_graph(subject, existing_graph):
    """Function takes a subject and an existing graph, returns a new graph with
    all predicate and objects of the existing graph copied to the new_graph with
    subject as the new subject

    Args:
        subject(rdflib.URIRef): A URIRef subject
        existing_graph(rdflib.Graph): A rdflib.Graph

    Returns:
        rdflib.Graph
    """
    new_graph = rdflib.Graph()
    for predicate, object_ in existing_graph.predicate_objects():
        new_graph.add((subject, predicate, object_))
    return new_graph