This documents the development version of NetworkX. Documentation for the current release can be found here.


lowest_common_ancestor(G, node1, node2, default=None)[source]

Compute the lowest common ancestor of the given pair of nodes.

  • G (NetworkX directed graph)

  • node1, node2 (nodes in the graph.)

  • default (object) – Returned if no common ancestor between node1 and node2


  • The lowest common ancestor of node1 and node2,

  • or default if they have no common ancestors.


Only defined on non-null directed acyclic graphs. Takes n log(n) time in the size of the graph. See all_pairs_lowest_common_ancestor when you have more than one pair of nodes of interest.