# sqlalchemy.exc.ArgumentError: Mutable default <list object at 0x...> for column 'tags' is not allowed. Use a callable instead.

- **ID:** `python/sqlalchemy-mutable-default-list`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Using a mutable object (like list or dict) as a default value in a Column, which can lead to shared state across instances.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   class Article(Base):
    __tablename__ = 'articles'
    tags = Column(JSON, default=list)  # or default=lambda: []
   ```

## Dead Ends

- **** — Lambda is not serializable and may cause issues with migrations. (30% fail)
- **** — Tuple is immutable but may not be suitable for all use cases. (50% fail)