python config_error ai_generated true

pydantic.errors.PydanticUserError: @computed_field should be used with @property. This error is raised when a @computed_field is applied to a non-property.

ID: python/pydantic-computed-field-serialization

Also available as: JSON · Markdown · 中文
80%Fix Rate
87%Confidence
0Evidence
2024-07-08First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

Decorator order was reversed: @computed_field placed above a plain method without @property, or @property placed above @computed_field.

generic

中文

装饰器顺序颠倒：@computed_field 放在了没有 @property 的普通方法之上，或 @property 放在了 @computed_field 之上。

Workarounds

  1. 95% success 
    from pydantic import BaseModel, computed_field
class M(BaseModel):
    a: int
    b: int
    @computed_field
    @property
    def total(self) -> int:
        return self.a + self.b
  2. 85% success 
    from pydantic import model_serializer
class M(BaseModel):
    a: int
    @model_serializer
    def ser(self):
        return {'a': self.a, 'double': self.a * 2}

Dead Ends

Common approaches that don't work:

  1. 60% fail

    Field no longer appears in model_dump / JSON output.

  2. 55% fail

    staticmethod returns a descriptor; validation raises because it is not a property.

  3. 50% fail

    Recomputes only at construction; stale if inputs mutate.