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topological_sort

topological_sort(G, nbunch=None, reverse=False)

Return a list of nodes in topological sort order.

A topological sort is a nonunique permutation of the nodes such that an edge from u to v implies that u appears before v in the topological sort order.

Parameters:

• G (NetworkX digraph) – A directed graph
• nbunch (container of nodes (optional)) – Explore graph in specified order given in nbunch
• reverse (bool, optional) – Return postorder instead of preorder if True. Reverse mode is a bit more efficient.

Raises:

• NetworkXError – Topological sort is defined for directed graphs only. If the graph G is undirected, a NetworkXError is raised.
• NetworkXUnfeasible – If G is not a directed acyclic graph (DAG) no topological sort exists and a NetworkXUnfeasible exception is raised.

Notes

This algorithm is based on a description and proof in The Algorithm Design Manual [1] .

See also

is_directed_acyclic_graph()

References

[1]	Skiena, S. S. The Algorithm Design Manual (Springer-Verlag, 1998). http://www.amazon.com/exec/obidos/ASIN/0387948600/ref=ase_thealgorithmrepo/