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on_chain_start() — langchain Function Reference

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

Function python Observability Tracers calls 4

Entity Profile

Dependency Diagram

graph TD
  6afc0657_d493_6ec0_9f7e_76a8658ef71c["on_chain_start()"]
  33d093c4_1ed0_fc6a_17c6_762d4c5cfa04["_AstreamEventsCallbackHandler"]
  6afc0657_d493_6ec0_9f7e_76a8658ef71c -->|defined in| 33d093c4_1ed0_fc6a_17c6_762d4c5cfa04
  411fc9b2_d611_6b33_d19f_de0162e13d29["_write_run_start_info()"]
  6afc0657_d493_6ec0_9f7e_76a8658ef71c -->|calls| 411fc9b2_d611_6b33_d19f_de0162e13d29
  87f79bee_f9c5_8262_1829_62f633c4f870["_send()"]
  6afc0657_d493_6ec0_9f7e_76a8658ef71c -->|calls| 87f79bee_f9c5_8262_1829_62f633c4f870
  9aed8e4f_9d4c_016f_aa43_c5908015cf8d["_get_parent_ids()"]
  6afc0657_d493_6ec0_9f7e_76a8658ef71c -->|calls| 9aed8e4f_9d4c_016f_aa43_c5908015cf8d
  8d2c2f35_3238_0aa3_4695_e986bf2b36bd["_assign_name()"]
  6afc0657_d493_6ec0_9f7e_76a8658ef71c -->|calls| 8d2c2f35_3238_0aa3_4695_e986bf2b36bd
  style 6afc0657_d493_6ec0_9f7e_76a8658ef71c fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/tracers/event_stream.py lines 549–595

    async 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,
    ) -> None:
        """Start a trace for a chain run."""
        name_ = _assign_name(name, serialized)
        run_type_ = run_type or "chain"

        data: EventData = {}

        # Work-around Runnable core code not sending input in some
        # cases.
        if inputs != {"input": ""}:
            data["input"] = inputs
            kwargs["inputs"] = inputs

        self._write_run_start_info(
            run_id,
            tags=tags,
            metadata=metadata,
            parent_run_id=parent_run_id,
            name_=name_,
            run_type=run_type_,
            **kwargs,
        )

        self._send(
            {
                "event": f"on_{run_type_}_start",
                "data": data,
                "name": name_,
                "tags": tags or [],
                "run_id": str(run_id),
                "metadata": metadata or {},
                "parent_ids": self._get_parent_ids(run_id),
            },
            run_type_,
        )

Domain

Subdomains

Defined In

Calls

Source

Frequently Asked Questions

What does on_chain_start() do?
on_chain_start() is a function in the langchain codebase, defined in libs/core/langchain_core/tracers/event_stream.py.
Where is on_chain_start() defined?
on_chain_start() is defined in libs/core/langchain_core/tracers/event_stream.py at line 549.
What does on_chain_start() call?
on_chain_start() calls 4 function(s): _assign_name, _get_parent_ids, _send, _write_run_start_info.

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