Return a pydot graph from a NetworkX graph N.
If N is a Graph or DiGraph, graphviz attributes can be supplied through the keyword arguments
node_attr: dictionary keyed by node to node attribute dictionary
edge_attr: dictionary keyed by edge tuple to edge attribute dictionary
If N is an XGraph or XDiGraph an attempt will be made first to copy properties attached to the graph (see from_pydot) and then updated with the calling arguments, if any.