561 Exceptions Bf96f8b9

---
title: Exceptions Module
path: src/tunacode/exceptions.py
type: file
depth: 0
description: Custom exception hierarchy for TunaCode
exports: [TunaCodeError, ToolExecutionError, ModelRetry, UserAbortError]
seams: [M]
---

# Exceptions Module

## Purpose
Defines a custom exception hierarchy for structured error handling throughout TunaCode.

## Exception Hierarchy

```
TunaCodeError (base)
├── ToolExecutionError
│   ├── FileOperationError
│   ├── CommandExecutionError
│   └── WebFetchError
├── ModelRetry
├── UserAbortError
├── ConfigurationError
├── StateError
└── GlobalRequestTimeoutError
```

## Exception Classes

### TunaCodeError
Base exception for all TunaCode errors:
- Provides consistent error type
- Allows catching all TunaCode errors
- Includes error context

### ToolExecutionError
Raised when tool execution fails:
- **bash** - Command failed or timed out
- **glob** - Pattern matching error
- **grep** - Search execution error
- **read_file** - File read failure
- **write_file** - File write failure
- **update_file** - File update failure
- **web_fetch** - HTTP request failure

**Attributes:**
- `tool_name` - Name of the tool
- `message` - Error description
- `original_error` - Underlying exception

### FileOperationError
Specialized for file system operations:
- FileNotFoundError handling
- PermissionError handling
- UnicodeDecodeError handling
- OSError handling

### ModelRetry
Signals the model should retry:
- Used for recoverable errors
- Triggers agent retry logic
- Provides retry guidance

**Common Causes:**
- Invalid file path
- Missing required arguments
- Temporary failures
- Retryable errors

### UserAbortError
Raised when user cancels operation:
- Ctrl+C during tool execution
- Confirmation rejection
- Session termination

### ConfigurationError
Configuration-related errors:
- Invalid config format
- Missing required settings
- Model not found
- Invalid template

### StateError
State management errors:
- Session load failure
- State corruption
- Invalid state transition

### GlobalRequestTimeoutError
Request timeout:
- Overall request exceeded timeout
- Agent iteration limit
- Unproductive limit reached

## Error Handling Strategy

**Tools Layer:**
```python
@base_tool
async def tool_func(...):
    try:
        # Tool logic
        pass
    except Exception as e:
        raise ToolExecutionError("tool_name", str(e))
```

**Agent Layer:**
```python
try:
    result = await tool_func(...)
except ToolExecutionError:
    # Log and continue
    pass
except ModelRetry:
    # Trigger retry
    pass
```

**UI Layer:**
```python
try:
    await process_request(...)
except UserAbortError:
    # Clean exit
    pass
except TunaCodeError as e:
    # Display error to user
    render_error(e)
```

## Error Messages

Exceptions that include guidance are formatted via a shared formatter in
`src/tunacode/exceptions.py` to keep output consistent and DRY. The formatter
builds a base message and appends optional sections in a fixed order.

**Section order:**
- Suggested fix
- More help
- Valid examples
- Recovery commands
- Troubleshooting steps

**Example output:**
```
Validation failed: Bad input

Suggested fix:
Use a valid value

Valid examples:
  - tunacode --help
  - tunacode --setup
```

## Integration Points

- **tools/decorators.py** - Error wrapping in decorators
- **core/agents/** - Error handling in agent loop
- **ui/renderers/errors.py** - Error display rendering
- **All modules** - Raise TunaCodeError exceptions

## Seams (M)

**Modification Points:**
- Add new exception types
- Extend error attributes
- Customize error messages
- Add error recovery strategies

**Best Practices:**
- Always wrap low-level exceptions
- Provide clear error messages
- Include context and suggestions
- Use appropriate exception type
- Never silently swallow errors