# pydantic_core._pydantic_core.ValidationError: 1 validation error for User
name
  Instance is frozen [type=frozen_instance, input_value='Bob', input_type=str]

- **ID:** `python/pydantic-immutable-frozen-assignment`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The model was declared with model_config = ConfigDict(frozen=True), so any attribute assignment after construction raises a frozen_instance error.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 2.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   new_user = user.model_copy(update={'name': 'Bob'})
   ```
2. **** (90% success)
   ```
   class User(BaseModel):
    model_config = ConfigDict(frozen=False)  # default
    name: str
   ```

## Dead Ends

- **** — Bypasses Pydantic's checks and produces an inconsistent model that violates __hash__ and equality guarantees. (75% fail)
- **** — Corrupts the model's internal fields storage and can raise KeyError or produce an invalid state. (85% fail)