affaan-m/ECC · error · ValueError

Failed to parse data

Error message

Failed to parse data: {data}

What it means

Illustrative exception-chaining example from the python-patterns skill: process_data's json.loads raised JSONDecodeError and it is re-raised as ValueError containing the raw data, with the original preserved via `from e`. The malformed data string is the input at fault.

Solutions

1. Include the decode error's position instead of echoing the whole payload
2. Truncate long data in the message to avoid log bloat
3. Distinguish malformed input from other ValueErrors with a dedicated exception type

When it happens

Trigger: Thrown at skills/python-patterns/SKILL.md:172 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of affaan-m/ECC@d8409a4b08 (2026-08-26). Data as JSON: /api/errors/3e635a90d5f90f1e. Report an issue: GitHub.

Appendix: source

Thrown at skills/python-patterns/SKILL.md:172

# Bad: Bare except
def load_config(path: str) -> Config:
    try:
        with open(path) as f:
            return Config.from_json(f.read())
    except:
        return None  # Silent failure!
```

### Exception Chaining

```python
def process_data(data: str) -> Result:
    try:
        parsed = json.loads(data)
    except json.JSONDecodeError as e:
        # Chain exceptions to preserve the traceback
        raise ValueError(f"Failed to parse data: {data}") from e
```

### Custom Exception Hierarchy

```python
class AppError(Exception):
    """Base exception for all application errors."""
    pass

class ValidationError(AppError):
    """Raised when input validation fails."""
    pass

class NotFoundError(AppError):
    """Raised when a requested resource is not found."""
    pass

# Usage

View on GitHub (pinned to d8409a4b08)