python runtime_error ai_generated partial

pydantic_core._pydantic_core.ValidationError: 1 validation error for Node children.0.children.0 RecursionError: maximum recursion depth exceeded while calling a Python object

ID: python/pydantic-recursion-error-self-referential

Also available as: JSON · Markdown · 中文
80%Fix Rate
82%Confidence
0Evidence
2025-01-19First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

A self-referential Pydantic model (tree/graph) was given a cyclic data structure, causing infinite recursion during validation. Pydantic has no built-in cycle detection for plain nested models.

generic

中文

自引用 Pydantic 模型（树/图）接收到循环数据结构，导致验证时无限递归。Pydantic 对普通嵌套模型没有内置的循环检测。

Workarounds

  1. 85% success 
    def break_cycles(obj, seen=None):
    seen = seen or set()
    if id(obj) in seen:
        return None
    seen.add(id(obj))
    if isinstance(obj, dict):
        return {k: break_cycles(v, seen) for k, v in obj.items()}
    if isinstance(obj, list):
        return [break_cycles(v, seen) for v in obj]
    return obj

Node.model_validate(break_cycles(raw))
  2. 70% success 
    from pydantic import BaseModel, field_validator

class Node(BaseModel):
    name: str
    children: list['Node'] = []

    @field_validator('children')
    @classmethod
    def limit_depth(cls, v):
        if len(v) > 100:
            raise ValueError('tree too deep')
        return v

Dead Ends

Common approaches that don't work:

  1. 80% fail

    This only defers the crash; a truly cyclic structure will still exhaust memory and eventually segfault the interpreter.

  2. 90% fail

    arbitrary_types_allowed permits non-Pydantic types, it does not detect or prevent cyclic references.