This documents an unmaintained version of NetworkX. Please upgrade to a maintained version and see the current NetworkX documentation.


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

Returns dictionary of predecessors in depth-first-search from source.

  • G (NetworkX graph)
  • source (node, optional) – Specify starting node for depth-first search and return edges in the component reachable from source.
  • depth_limit (int, optional (default=len(G))) – Specify the maximum search depth.

pred – A dictionary with nodes as keys and predecessor nodes as values.

Return type:



>>> G = nx.path_graph(4)
>>> nx.dfs_predecessors(G, source=0)
{1: 0, 2: 1, 3: 2}
>>> nx.dfs_predecessors(G, source=0, depth_limit=2)
{1: 0, 2: 1}


If a source is not specified then a source is chosen arbitrarily and repeatedly until all components in the graph are searched.

The implementation of this function is adapted from David Eppstein’s depth-first search function in PADS, with modifications to allow depth limits based on the Wikipedia article “Depth-limited search”.