FastAPI · interview question

What is the healthiest performance judgment around validation?

Multiple choiceMediumchapter-13-curatedpremiumfastapivalidation

python

class CreateOrderRequest(BaseModel):
    sku: str
    quantity: int

    @field_validator("quantity")
    @classmethod
    def quantity_must_be_positive(cls, value: int) -> int:
        if value <= 0:
            raise ValueError("quantity must be positive")
        return value

Measure before optimizing, then change the part that actually dominates cost instead of guessing from style alone.Solve the symptom with comments only and avoid changing the code shape around validation.Delay clarity until production traffic reveals the edge case and then patch it under pressure.Keep validation implicit so the script stays short and hope the next engineer infers the rule.

Answer and explanation

Correct answer

A. Measure before optimizing, then change the part that actually dominates cost instead of guessing from style alone.

Why

Premature optimization is usually weaker than targeted optimization backed by measurement.

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What is the healthiest performance judgment around validation?

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