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ChatOpenAI

As explained in Build Python Web Apps with Streamlit

ChatOpenAI is a LangChain class that provides an interface to OpenAI chat language models.

ChatOpenAI is a LangChain class for calling an OpenAI chat model. In a chatbot, it can supply the response-generating step of a LangGraph graph. section 10.2.3

Call the model from a graph node

Create the model with `ChatOpenAI(model_name="gpt-5.1", openai_api_key=...)`. The assistant node passes its message list to `llm.invoke(messages)`, then adds the returned AI message to the graph state. A user message starts the graph; the final message supplies the reply. section 10.2.3

For a Streamlit chatbot, the bot can receive an API key from Streamlit secrets, construct ChatOpenAI with a `max_tokens` setting, and pass it to the graph. This keeps model setup separate from the chat interface. section 10.2.3

How Build Python Web Apps with Streamlit covers it

How deep it goes
Shows model construction and invocation inside working graph and chatbot examples, without detailing ChatOpenAI internals.
Examples
Uses a one-node command-line chatbot and a Streamlit chatbot that displays the model’s reply.
What it assumes
Introduces message roles and TypedDict graph state while using Python imports, classes, and functions.
What you can do after
Apply it via LangChain and LangGraph to generate a chatbot reply from a list of messages.
How it connects
Connects LangChain chat models to LangGraph state, message roles, and a Streamlit chat interface.

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This explainer was generated by Manning's knowledge graph from the text of Build Python Web Apps with Streamlit. The section links point to the parts of the book it draws on.