# networkx.algorithms.shortest_paths.generic.shortest_path_length¶

shortest_path_length(G, source=None, target=None, weight=None, method='dijkstra')[source]

Compute shortest path lengths in the graph.

Parameters
• G (NetworkX graph)

• source (node, optional) – Starting node for path. If not specified, compute shortest path lengths using all nodes as source nodes.

• target (node, optional) – Ending node for path. If not specified, compute shortest path lengths using all nodes as target nodes.

• weight (None or string, optional (default = None)) – If None, every edge has weight/distance/cost 1. If a string, use this edge attribute as the edge weight. Any edge attribute not present defaults to 1.

• method (string, optional (default = ‘dijkstra’)) – The algorithm to use to compute the path length. Supported options: ‘dijkstra’, ‘bellman-ford’. Other inputs produce a ValueError. If weight is None, unweighted graph methods are used, and this suggestion is ignored.

Returns

length – If the source and target are both specified, return the length of the shortest path from the source to the target.

If only the source is specified, return a dict keyed by target to the shortest path length from the source to that target.

If only the target is specified, return a dict keyed by source to the shortest path length from that source to the target.

If neither the source nor target are specified, return an iterator over (source, dictionary) where dictionary is keyed by target to shortest path length from source to that target.

Return type

int or iterator

Raises
• NodeNotFound – If source is not in G.

• NetworkXNoPath – If no path exists between source and target.

• ValueError – If method is not among the supported options.

Examples

>>> G = nx.path_graph(5)
>>> nx.shortest_path_length(G, source=0, target=4)
4
>>> p = nx.shortest_path_length(G, source=0) # target not specified
>>> p[4]
4
>>> p = nx.shortest_path_length(G, target=4) # source not specified
>>> p[0]
4
>>> p = dict(nx.shortest_path_length(G)) # source,target not specified
>>> p[0][4]
4


Notes

The length of the path is always 1 less than the number of nodes involved in the path since the length measures the number of edges followed.

For digraphs this returns the shortest directed path length. To find path lengths in the reverse direction use G.reverse(copy=False) first to flip the edge orientation.

all_pairs_shortest_path_length(), all_pairs_dijkstra_path_length(), all_pairs_bellman_ford_path_length(), single_source_shortest_path_length(), single_source_dijkstra_path_length(), single_source_bellman_ford_path_length()