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skills/langgraph-master/example_basic_chatbot.md

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+# Basic Chatbot
+
+Implementation example of a basic chatbot using LangGraph.
+
+## Complete Code
+
+```python
+from typing import Annotated
+from langgraph.graph import StateGraph, START, END, MessagesState
+from langgraph.graph.message import add_messages
+from langgraph.checkpoint.memory import MemorySaver
+from langchain_anthropic import ChatAnthropic
+
+# 1. Initialize LLM
+llm = ChatAnthropic(model="claude-sonnet-4-5-20250929")
+
+# 2. Define node
+def chatbot_node(state: MessagesState):
+    """Chatbot node"""
+    response = llm.invoke(state["messages"])
+    return {"messages": [response]}
+
+# 3. Build graph
+builder = StateGraph(MessagesState)
+builder.add_node("chatbot", chatbot_node)
+builder.add_edge(START, "chatbot")
+builder.add_edge("chatbot", END)
+
+# 4. Compile with checkpointer
+checkpointer = MemorySaver()
+graph = builder.compile(checkpointer=checkpointer)
+
+# 5. Execute
+config = {"configurable": {"thread_id": "conversation-1"}}
+
+while True:
+    user_input = input("User: ")
+    if user_input.lower() in ["quit", "exit", "q"]:
+        break
+
+    # Send message
+    for chunk in graph.stream(
+        {"messages": [{"role": "user", "content": user_input}]},
+        config,
+        stream_mode="values"
+    ):
+        chunk["messages"][-1].pretty_print()
+```
+
+## Explanation
+
+### 1. MessagesState
+
+```python
+from langgraph.graph import MessagesState
+
+# MessagesState is equivalent to:
+class MessagesState(TypedDict):
+    messages: Annotated[list[AnyMessage], add_messages]
+```
+
+- `messages`: List of messages
+- `add_messages`: Reducer that adds new messages
+
+### 2. Checkpointer
+
+```python
+from langgraph.checkpoint.memory import MemorySaver
+
+checkpointer = MemorySaver()
+graph = builder.compile(checkpointer=checkpointer)
+```
+
+- Saves conversation state
+- Continues conversation with same `thread_id`
+
+### 3. Streaming
+
+```python
+for chunk in graph.stream(input, config, stream_mode="values"):
+    chunk["messages"][-1].pretty_print()
+```
+
+- `stream_mode="values"`: Complete state after each step
+- `pretty_print()`: Displays messages in a readable format
+
+## Extension Examples
+
+### Adding System Message
+
+```python
+def chatbot_with_system(state: MessagesState):
+    """With system message"""
+    system_msg = {
+        "role": "system",
+        "content": "You are a helpful assistant."
+    }
+
+    response = llm.invoke([system_msg] + state["messages"])
+    return {"messages": [response]}
+```
+
+### Limiting Message History
+
+```python
+def chatbot_with_limit(state: MessagesState):
+    """Use only the latest 10 messages"""
+    recent_messages = state["messages"][-10:]
+    response = llm.invoke(recent_messages)
+    return {"messages": [response]}
+```
+
+## Related Pages
+
+- [01_core_concepts_overview.md](01_core_concepts_overview.md) - Understanding fundamental concepts
+- [03_memory_management_overview.md](03_memory_management_overview.md) - Checkpointer details
+- [example_rag_agent.md](example_rag_agent.md) - More advanced example