This will create a new PyDiGraph object from this
graph. All edges in this graph will result in a bidirectional edge
pair in the output graph.
Note
The node indices in the output PyDiGraph may
differ if nodes have been removed.
Returns:
A new PyDiGraph object with a
bidirectional edge pair for each edge in this graph. Also all
node and edge weights/data payloads are copied by reference to
the output graph