Python's TypedDict: Structure, Compatibility, and Trade-offs

The source provides an extensive guide to Python's typing.TypedDict, which is a type hint used for statically checking dictionaries with a fixed and heterogeneous structure, commonly used for modeling JSON data or configuration files. It explains that TypedDict is a typing-only construct that offers zero runtime overhead because the resulting object is simply a standard Python dict at execution time, which is its primary advantage and limitation. The document details the evolution of key management, from the original total parameter to the introduction of Required and NotRequired (PEP 655) for granular control over optionality. Furthermore, it addresses structural subtyping rules, emphasizing that TypedDict is intentionally incompatible with the mutable generic dict type to preserve schema integrity, and it covers advanced features like the ReadOnly qualifier (PEP 705) and controlling schema openness with closed=True (PEP 728). Finally, the text offers an architectural comparison, concluding that while TypedDict is ideal for highly performant, trusted data, external validation libraries like Pydantic are necessary for handling untrusted external data due to the lack of runtime validation.