Python · correctness

invalid-pydantic-field-default

python:invalid-pydantic-field-default

Require literal Pydantic `Field` defaults to satisfy their declared contract.

Code: SARJ400
Default: error
Fix: none
Languages: python

Why

An invalid default lets a model begin with a value that contradicts its annotation or field bounds, moving a deterministic configuration error into runtime validation.

Fix

Choose a default allowed by the annotation and every literal `Field` bound, or widen the contract when the value is intentional.

Before / after

Executed by this rule’s unit tests.

Before

Default is outside the declared field bounds

app/models.py · focus

from pydantic import BaseModel, Field

class RetryPolicy(BaseModel):
    attempts: int = Field(default=0, gt=0)

After

Default satisfies the declared field bounds

app/models.py · focus

from pydantic import BaseModel, Field

class RetryPolicy(BaseModel):
    attempts: int = Field(default=1, gt=0)

Limits

The rule checks direct public fields on classes that directly inherit Pydantic `BaseModel`.
It reports only statically provable literal conflicts with nullability, `Literal` domains, and numeric or string-length bounds.
Test and generated files are excluded.