python type_error ai_generated true

pydantic_core._pydantic_core.ValidationError: 1 validation error for Product price Input should be a valid string [type=string_type, input_value=19.99, input_type=float]

ID: python/pydantic-v2-string-type-coercion-strict

Also available as: JSON · Markdown · 中文
80%Fix Rate
86%Confidence
0Evidence
2024-05-02First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

The model was configured with strict=True (or the field uses StrictStr), so Pydantic v2 refuses to coerce a float into a string even though lax mode would accept it.

generic

中文

模型配置了 strict=True（或字段使用了 StrictStr），因此 Pydantic v2 拒绝将 float 强制转换为字符串，即使宽松模式会接受。

Workarounds

  1. 93% success 
    Add a field_validator with mode='before' to coerce: `@field_validator('price', mode='before') @classmethod def coerce(cls, v): return str(v)`
  2. 90% success 
    Relax strictness per-field: `price: str = Field(strict=False)` while keeping the model strict.

Dead Ends

Common approaches that don't work:

  1. 60% fail

    Pushes type-handling logic to every call site; easy to miss one and re-trigger the error

  2. 70% fail

    Disables strictness everywhere, silently accepting bad data for unrelated fields