NetworkXDialect does not work correctly with networkx.DiGraph

[khoale88]

Hi @j6k4m8,

There is an issue with grand.Graph and grand.dialects.NetworkXDialect.

Since NetworkXDialect is inherited from networkx.Graph, there happen to be discrepancies between grand.dialects.NetworkXDialect and networkx.Digraph which is popagated back to grand.Graph. One of them is the networkx.Graph.edges returns EdgeView while networkx.Digraph.edges returns OutEdgeView.

Below is one of the test to replicate the issue

def test_nx_edges(self):
        G = Graph(directed=True).nx
        H = nx.DiGraph()
        G.add_edge("1", "2")
        G.add_edge("2", "1")   # <<< this won't work with EdgeView for G
        G.add_edge("1", "3")
        H.add_edge("1", "2")
        H.add_edge("2", "1")   # <<< OutEdgeView returns this for H
        H.add_edge("1", "3")
        self.assertEqual(dict(G.edges), dict(H.edges))
        self.assertEqual(dict(G.edges()), dict(H.edges()))
        self.assertEqual(list(G.edges["1", "2"]), list(H.edges["1", "2"]))

The result is

    def test_nx_edges(self):
        G = Graph(directed=True).nx
        H = nx.DiGraph()
        # H = nx.Graph()
        G.add_edge("1", "2")
        G.add_edge("2", "1")
        G.add_edge("1", "3")
        H.add_edge("1", "2")
        H.add_edge("2", "1")
        H.add_edge("1", "3")
>       self.assertEqual(dict(G.edges), dict(H.edges))
E       AssertionError: {('1', '2'): {}, ('1', '3'): {}} != {('1', '2'): {}, ('1', '3'): {}, ('2', '1'): {}}
E       - {('1', '2'): {}, ('1', '3'): {}}
E       + {('1', '2'): {}, ('1', '3'): {}, ('2', '1'): {}}
E       ?                              ++++++++++++++++