{
  "id": "python/pydantic-field-info-missing-default",
  "signature": "TypeError: FieldInfo.__init__() got an unexpected keyword argument 'default_factory' when used with a positional default in Field(...)",
  "signature_zh": "TypeError: FieldInfo.__init__() 收到意外的关键字参数 'default_factory'",
  "regex": "TypeError:\\ FieldInfo\\.__init__\\(\\)\\ got\\ an\\ unexpected\\ keyword\\ argument\\ 'default_factory'\\ when\\ used\\ with\\ a\\ positional\\ default\\ in\\ Field\\(\\.\\.\\.\\)",
  "domain": "python",
  "category": "type_error",
  "subcategory": null,
  "root_cause": "Field() is called with both a positional default value and default_factory, which is ambiguous and rejected by Pydantic v2's stricter FieldInfo signature.",
  "root_cause_type": "generic",
  "root_cause_zh": "Field() 同时传入了位置默认值和 default_factory，存在歧义，被 Pydantic v2 更严格的 FieldInfo 签名拒绝。",
  "versions": [
    {
      "version": "2.x",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    }
  ],
  "os_specific": {},
  "dead_ends": [
    {
      "action": "",
      "why_fails": "Raises TypeError at import time before any model is instantiated.",
      "fail_rate": 0.9,
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "why_fails": "Breaks immutability guarantees and validation order; often still yields None when callers inspect the field.",
      "fail_rate": 0.5,
      "condition": "",
      "sources": []
    }
  ],
  "workarounds": [
    {
      "action": "",
      "success_rate": 0.98,
      "how": "Use only default_factory:\n\nclass M(BaseModel):\n    items: list[int] = Field(default_factory=list)",
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "success_rate": 0.85,
      "how": "Or use only a positional default:\n\nclass M(BaseModel):\n    items: list[int] = []  # careful: mutable default is copied by pydantic",
      "condition": "",
      "sources": []
    }
  ],
  "workarounds_zh": [],
  "transition_graph": {
    "leads_to": [],
    "preceded_by": [],
    "frequently_confused_with": []
  },
  "official_doc_url": null,
  "official_doc_section": null,
  "error_code": null,
  "verification_tier": "ai_generated",
  "confidence": 0.84,
  "fix_success_rate": 0.8,
  "resolvable": "true",
  "first_seen": "2024-05-08",
  "last_confirmed": "2025-01-01",
  "last_updated": "2025-01-01",
  "evidence_count": 0,
  "tags": [],
  "locale": "en",
  "aliases": []
}