LangChain Python quickstart

Follow the live docs — do not invent an alternate API from memory:

https://docs.langchain.com/oss/python/langchain/quickstart

Fetch that page (Docs MCP or HTTP) and implement what it shows (weather agent + create_agent).

Local setup constraints

Apply these on top of the quickstart (they keep setup minimal and model-agnostic):

1. Ask which provider/model to use. Showcase that LangChain is model-agnostic. Suggested prompt:

   Which model should this agent use? Pass a provider:model string — e.g. openai:gpt-5.5, anthropic:claude-sonnet-5, google_genai:gemini-2.5-flash-lite. Default if you're unsure: anthropic:claude-sonnet-5.

   Swap the quickstart's model string for their choice (or the default).

2. Create a new directory (e.g. langchain-agent/) and do all work there — do not pollute the open project.