{
  "id": "python/pydantic-union-type-validation",
  "signature": "pydantic.errors.UnionError: Unable to validate input for union",
  "signature_zh": "pydantic.errors.UnionError: 无法为联合类型验证输入",
  "regex": "pydantic\\.errors\\.UnionError:\\ Unable\\ to\\ validate\\ input\\ for\\ union",
  "domain": "python",
  "category": "type_error",
  "subcategory": null,
  "root_cause": "When a field is typed as Union[A, B], Pydantic tries each type in order; if none match, it raises UnionError, often due to ambiguous types or strict validation.",
  "root_cause_type": "generic",
  "root_cause_zh": "当字段类型为 Union[A, B] 时，Pydantic 会按顺序尝试每种类型；如果都不匹配，就会抛出 UnionError，通常是由于类型歧义或严格验证。",
  "versions": [
    {
      "version": "2.x",
      "introduced": null,
      "deprecated": null,
      "removed": null,
      "behavior_change": null,
      "status": "active"
    }
  ],
  "os_specific": {},
  "dead_ends": [
    {
      "action": "",
      "why_fails": "Order matters; if first type accepts too broadly, it may consume valid inputs for second type.",
      "fail_rate": 0.7,
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "why_fails": "Optional[Union] can still fail if input is None but not allowed.",
      "fail_rate": 0.6,
      "condition": "",
      "sources": []
    }
  ],
  "workarounds": [
    {
      "action": "",
      "success_rate": 0.9,
      "how": "Use discriminated unions with Literal types: Field(discriminator='type')",
      "condition": "",
      "sources": []
    },
    {
      "action": "",
      "success_rate": 0.85,
      "how": "Define a custom validator to handle complex union logic",
      "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": 0.83,
  "fix_success_rate": 0.8,
  "resolvable": "true",
  "first_seen": "2024-05-05",
  "last_confirmed": "2025-01-01",
  "last_updated": "2025-01-01",
  "evidence_count": 0,
  "tags": [],
  "locale": "en",
  "aliases": []
}