on_chain_start() — langchain Function Reference

Architecture documentation for the on_chain_start() function in base.py from the langchain codebase.

Function python Observability Tracers calls 3 called by 1

Entity Profile

Observability→ Tracers→ on_chain_start() — langchain Function Reference

Dependency Diagram

graph TD
  9d98e4df_1dff_cdb6_b489_397648f5aa8a["on_chain_start()"]
  0f6b3261_31fa_c34e_ca33_cb141bdf78ff["BaseTracer"]
  9d98e4df_1dff_cdb6_b489_397648f5aa8a -->|defined in| 0f6b3261_31fa_c34e_ca33_cb141bdf78ff
  4fc30b16_7ae1_9cd3_3e1a_cab2c2a53122["on_chain_start()"]
  4fc30b16_7ae1_9cd3_3e1a_cab2c2a53122 -->|calls| 9d98e4df_1dff_cdb6_b489_397648f5aa8a
  e367264b_d5e2_1e7f_2b3a_e362236bcd24["_start_trace()"]
  9d98e4df_1dff_cdb6_b489_397648f5aa8a -->|calls| e367264b_d5e2_1e7f_2b3a_e362236bcd24
  0983c53e_c9c4_70ff_cd08_6f356740fd06["_on_chain_start()"]
  9d98e4df_1dff_cdb6_b489_397648f5aa8a -->|calls| 0983c53e_c9c4_70ff_cd08_6f356740fd06
  4fc30b16_7ae1_9cd3_3e1a_cab2c2a53122["on_chain_start()"]
  9d98e4df_1dff_cdb6_b489_397648f5aa8a -->|calls| 4fc30b16_7ae1_9cd3_3e1a_cab2c2a53122
  style 9d98e4df_1dff_cdb6_b489_397648f5aa8a fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/tracers/base.py lines 241–283

    def on_chain_start(
        self,
        serialized: dict[str, Any],
        inputs: dict[str, Any],
        *,
        run_id: UUID,
        tags: list[str] | None = None,
        parent_run_id: UUID | None = None,
        metadata: dict[str, Any] | None = None,
        run_type: str | None = None,
        name: str | None = None,
        **kwargs: Any,
    ) -> Run:
        """Start a trace for a chain run.

        Args:
            serialized: The serialized chain.
            inputs: The inputs for the chain.
            run_id: The run ID.
            tags: The tags for the run.
            parent_run_id: The parent run ID.
            metadata: The metadata for the run.
            run_type: The type of the run.
            name: The name of the run.
            **kwargs: Additional arguments.

        Returns:
            The run.
        """
        chain_run = self._create_chain_run(
            serialized=serialized,
            inputs=inputs,
            run_id=run_id,
            tags=tags,
            parent_run_id=parent_run_id,
            metadata=metadata,
            run_type=run_type,
            name=name,
            **kwargs,
        )
        self._start_trace(chain_run)
        self._on_chain_start(chain_run)
        return chain_run