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How does Pydantic v2 validation work (BaseModel, field_validator, mode)?

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01

Understand the problem

Pydantic v2 patterns trending in 2025-26 FastAPI codebases.

pydanticvalidationpython3.11
02

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Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

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Pydantic v2 validates via Rust core (pydantic-core), with mode='before'/'after', Annotated types, and field_validator/model_validator.

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