_last_node() — langchain Function Reference

Architecture documentation for the _last_node() function in graph.py from the langchain codebase.

Function python LangChainCore Runnables called by 2

Entity Profile

LangChainCore→ Runnables→ _last_node() — langchain Function Reference

Dependency Diagram

graph TD
  6607eba9_2327_f10b_2f7a_81bdd9ce1d84["_last_node()"]
  81a6280b_4752_84db_f1fa_1a3b8040d481["graph.py"]
  6607eba9_2327_f10b_2f7a_81bdd9ce1d84 -->|defined in| 81a6280b_4752_84db_f1fa_1a3b8040d481
  6b97cc3d_1205_0325_4d44_e903570471b2["last_node()"]
  6b97cc3d_1205_0325_4d44_e903570471b2 -->|calls| 6607eba9_2327_f10b_2f7a_81bdd9ce1d84
  5ce5505c_4a08_f190_13f7_65b75fa4fde9["trim_last_node()"]
  5ce5505c_4a08_f190_13f7_65b75fa4fde9 -->|calls| 6607eba9_2327_f10b_2f7a_81bdd9ce1d84
  style 6607eba9_2327_f10b_2f7a_81bdd9ce1d84 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/runnables/graph.py lines 724–739

def _last_node(graph: Graph, exclude: Sequence[str] = ()) -> Node | None:
    """Find the single node that is not a source of any edge.

    Exclude nodes/targets with IDs in the exclude list.

    If there is no such node, or there are multiple, return `None`.

    When drawing the graph, this node would be the destination.
    """
    sources = {edge.source for edge in graph.edges if edge.target not in exclude}
    found: list[Node] = [
        node
        for node in graph.nodes.values()
        if node.id not in exclude and node.id not in sources
    ]
    return found[0] if len(found) == 1 else None