# networkx.algorithms.traversal.breadth_first_search.bfs_predecessors¶

bfs_predecessors(G, source, depth_limit=None)[source]

Returns an iterator of predecessors in breadth-first-search from source.

Parameters
• G (NetworkX graph)

• source (node) – Specify starting node for breadth-first search

• depth_limit (int, optional(default=len(G))) – Specify the maximum search depth

Returns

pred – (node, predecessors) iterator where predecessors is the list of predecessors of the node.

Return type

iterator

Examples

>>> G = nx.path_graph(3)
>>> print(dict(nx.bfs_predecessors(G, 0)))
{1: 0, 2: 1}
>>> H = nx.Graph()
>>> H.add_edges_from([(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)])
>>> print(dict(nx.bfs_predecessors(H, 0)))
{1: 0, 2: 0, 3: 1, 4: 1, 5: 2, 6: 2}
>>> M = nx.Graph()
>>> nx.add_path(M, [0, 1, 2, 3, 4, 5, 6])
>>> nx.add_path(M, [2, 7, 8, 9, 10])
>>> print(sorted(nx.bfs_predecessors(M, source=1, depth_limit=3)))
[(0, 1), (2, 1), (3, 2), (4, 3), (7, 2), (8, 7)]


Notes

Based on http://www.ics.uci.edu/~eppstein/PADS/BFS.py by D. Eppstein, July 2004. The modifications to allow depth limits based on the Wikipedia article “Depth-limited-search”.

See also

bfs_tree(), bfs_edges(), edge_bfs()