2025-08-19 Tue

• #TIL
  • Today, while attempting to use Pydantic/Dynamic Model Creation in conjunction with langgraph/config/runtime (see also Pydantic'c docs on "The Annotated Pattern")I Learned that Annotated is variadic in python.

  • typing — Support for type hints — Python 3.9.23 documentation: 
    A type, introduced in PEP 593 (Flexible function and variable annotations), to decorate existing types with context-specific metadata (possibly multiple pieces of it, as Annotated is variadic).
    

  • As a result, this is legal and possible:

    • Annotated[
        Literal["anthropic/claude-3-7-sonnet-latest", "openai/gpt-4o-mini"],
        {"__template_metadata__": {"kind": "llm"}},
        pydantic.Field(...)
      ]