graph_longest_simple_path(graph, /)#

Return a longest simple path in the graph

This function searches computes all pairs of all simple paths and returns a path of the longest length from that set. It is roughly equivalent to running something like:

from rustworkx import all_pairs_all_simple_paths

simple_path_pairs = rx.all_pairs_all_simple_paths(graph)
longest_path = max(
    (u for y in simple_path_pairs.values() for z in y.values() for u in z),
    key=lambda x: len(x),

but this function will be more efficient than using max() as the search is evaluated in parallel before returning to Python. In the case of multiple paths of the same maximum length being present in the graph only one will be provided. There are no guarantees on which of the multiple longest paths will be returned (as it is determined by the parallel execution order). This is a tradeoff to improve runtime performance. If a stable return is required in such case consider using the max() equivalent above instead.

This function is multithreaded and will launch a thread pool with threads equal to the number of CPUs by default. You can tune the number of threads with the RAYON_NUM_THREADS environment variable. For example, setting RAYON_NUM_THREADS=4 would limit the thread pool to 4 threads.


graph (PyGraph) – The graph to find the longest path in


A sequence of node indices that represent the longest simple graph found in the graph. If the graph is empty None will be returned instead.

Return type: