python data_error ai_generated true

pydantic_core._pydantic_core.ValidationError: 1 validation error for User name Field required [type=missing, input_value={'age': 25}, input_type=dict]

ID: python/pydantic-validation-error-field-required

Also available as: JSON · Markdown · 中文
80%Fix Rate
90%Confidence
0Evidence
2024-03-12First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

A required field is missing from the input data when instantiating a Pydantic model. In Pydantic v2, missing fields raise ValidationError instead of silently defaulting.

generic

中文

实例化 Pydantic 模型时输入数据缺少必填字段。在 Pydantic v2 中，缺失字段会抛出 ValidationError，而不是静默使用默认值。

Workarounds

  1. 95% success 
    from typing import Optional
from pydantic import BaseModel

class User(BaseModel):
    name: Optional[str] = None
    age: int
  2. 98% success 
    user = User(name='Alice', age=25)  # include all required fields
# or
User.model_validate({'name': 'Alice', 'age': 25})

Dead Ends

Common approaches that don't work:

  1. 85% fail

    Silently swallowing ValidationError means downstream code receives an object with missing attributes, causing AttributeError later.

  2. 70% fail

    Pydantic v2 models are immutable by default and reject attribute assignment unless model_config allows it.