Add `langchain` agent (#22)

* Add `langchain` agent

* Add langchain to api.md

* fix(tests): Add missing `langchain`.

.github/workflows/tests.yaml

@@ -28,7 +28,7 @@ jobs:
           cache: "pip"
 
       - name: Install
-        run: pip install -e '.[arize,smolagents,openai,tests]'
+        run: pip install -e '.[arize,langchain,smolagents,openai,tests]'
 
       - name: Run tests
         run: pytest -v tests

docs/api.md

@@ -8,6 +8,8 @@
 
 ::: surf_spot_finder.agents.RUNNERS
 
+::: surf_spot_finder.agents.langchain
+
 ::: surf_spot_finder.agents.openai
 
 ::: surf_spot_finder.agents.smolagents

examples/langchain_single_agent.yaml

@@ -0,0 +1,9 @@
+location: Pontevedra
+date: 2025-03-22 12:00
+max_driving_hours: 2
+model_id: o3-mini
+agent_type: langchain
+tools:
+ - "surf_spot_finder.tools.search_web"
+ - "surf_spot_finder.tools.visit_webpage"
+# input_prompt_template:

pyproject.toml

@@ -17,6 +17,11 @@ dependencies = [
 ]
 
 [project.optional-dependencies]
+langchain = [
+  "langchain",
+  "langgraph",
+  "openinference-instrumentation-langchain"
+]
 smolagents = [
   "smolagents[litellm]>=1.10.0",
   "openinference-instrumentation-smolagents>=0.1.4"

src/surf_spot_finder/agents/__init__.py

@@ -1,7 +1,9 @@
+from .langchain import run_lanchain_agent
 from .openai import run_openai_agent, run_openai_multi_agent
 from .smolagents import run_smolagent
 
 RUNNERS = {
+    "langchain": run_lanchain_agent,
     "openai": run_openai_agent,
     "smolagents": run_smolagent,
     "openai_multi_agent": run_openai_multi_agent,

src/surf_spot_finder/agents/langchain.py

@@ -0,0 +1,64 @@
+import inspect
+import importlib
+
+from loguru import logger
+
+try:
+    from langchain.chat_models import init_chat_model
+    from langchain_core.messages import HumanMessage
+    from langchain_core.tools import BaseTool, tool
+    from langgraph.checkpoint.memory import MemorySaver
+    from langgraph.prebuilt import create_react_agent
+
+    langchain_available = True
+except ImportError:
+    langchain_available = False
+
+
+@logger.catch(reraise=True)
+def run_lanchain_agent(
+    model_id: str, prompt: str, tools: list[str] | None = None, **kwargs
+):
+    """Runs an langchain ReAct agent with the given prompt and configuration.
+
+    Uses [create_react_agent](https://langchain-ai.github.io/langgraph/reference/prebuilt/#langgraph.prebuilt.chat_agent_executor.create_react_agent).
+
+    Args:
+        model_id: The ID of the model to use.
+            See [init_chat_model](https://python.langchain.com/api_reference/langchain/chat_models/langchain.chat_models.base.init_chat_model.html).
+        prompt: The prompt to be given to the agent.
+    """
+    if not langchain_available:
+        raise ImportError(
+            "You need to `pip install langchain langgraph` to use this agent"
+        )
+
+    if tools is None:
+        tools = [
+            "surf_spot_finder.tools.search_web",
+            "surf_spot_finder.tools.visit_webpage",
+        ]
+
+    imported_tools = []
+    for imported_tool in tools:
+        module, func = imported_tool.rsplit(".", 1)
+        module = importlib.import_module(module)
+        imported_tool = getattr(module, func)
+        if inspect.isclass(imported_tool):
+            imported_tool = imported_tool()
+        if not isinstance(imported_tool, BaseTool):
+            imported_tool = tool(imported_tool)
+        imported_tools.append((imported_tool))
+
+    model = init_chat_model(model_id)
+    agent = create_react_agent(
+        model=model,
+        tools=imported_tools,
+        checkpointer=MemorySaver(),
+    )
+    for step in agent.stream(
+        {"messages": [HumanMessage(content=prompt)]},
+        {"configurable": {"thread_id": "abc123"}},
+        stream_mode="values",
+    ):
+        step["messages"][-1].pretty_print()

src/surf_spot_finder/tracing.py

@@ -104,3 +104,7 @@ def setup_tracing(tracer_provider: TracerProvider, agent_type: str) -> None:
         from openinference.instrumentation.smolagents import SmolagentsInstrumentor
 
         SmolagentsInstrumentor().instrument(tracer_provider=tracer_provider)
+    elif agent_type == "langchain":
+        from openinference.instrumentation.langchain import LangChainInstrumentor
+
+        LangChainInstrumentor().instrument(tracer_provider=tracer_provider)

tests/unit/agents/test_unit_langchain.py

@@ -0,0 +1,33 @@
+from unittest.mock import patch, MagicMock
+
+from surf_spot_finder.agents.langchain import (
+    run_lanchain_agent,
+)
+from surf_spot_finder.tools import (
+    search_web,
+    visit_webpage,
+)
+
+
+def test_run_langchain_agent_default():
+    model_mock = MagicMock()
+    create_mock = MagicMock()
+    agent_mock = MagicMock()
+    create_mock.return_value = agent_mock
+    memory_mock = MagicMock()
+    tool_mock = MagicMock()
+
+    with (
+        patch("surf_spot_finder.agents.langchain.create_react_agent", create_mock),
+        patch("surf_spot_finder.agents.langchain.init_chat_model", model_mock),
+        patch("surf_spot_finder.agents.langchain.MemorySaver", memory_mock),
+        patch("surf_spot_finder.agents.langchain.tool", tool_mock),
+    ):
+        run_lanchain_agent("gpt-4o", "Test prompt")
+        model_mock.assert_called_once_with("gpt-4o")
+        create_mock.assert_called_once_with(
+            model=model_mock.return_value,
+            tools=[tool_mock(search_web), tool_mock(visit_webpage)],
+            checkpointer=memory_mock.return_value,
+        )
+        agent_mock.stream.assert_called_once()