Derives: Comparison (Reference)

This page documents Eq, Ord, and Hash.

See also:

• Derives & traits
• Customize derived behavior (How-to)

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Eq (equality)

• Enables: ==, !=
• Default behavior: structural, field-based equality
• Custom behavior: define __eq__(self, other: Self) -> bool
• Conflict rule: if you define __eq__, do not also @derive(Eq)

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Ord (ordering)

• Enables: <, <=, >, >=, sorted(...)
• Default behavior: structural ordering by field order
• Custom behavior: define __lt__(self, other: Self) -> bool
• Conflict rule: if you define __lt__, do not also @derive(Ord)

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Hash

• Enables: use as Set members and Dict keys
• Default behavior: structural, field-based hashing
• Custom behavior: define __hash__(self) -> int
• Conflict rule: if you define __hash__, do not also @derive(Hash)

Consistency rule:

• If a == b, then a.__hash__() == b.__hash__().

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Tie-breakers (ordering)

If you implement __lt__, avoid “accidental ties” by adding a deterministic tie-breaker:

model Task:
    priority: int
    name: str

    def __lt__(self, other: Task) -> bool:
        if self.priority != other.priority:
            return self.priority < other.priority
        return self.name < other.name