Error Types
Complete reference for Python exception types and error handling. Understanding different error types helps you write more robust code and debug issues effectively.
BaseException
├── SystemExit
├── KeyboardInterrupt
├── GeneratorExit
└── Exception
├── StopIteration
├── StopAsyncIteration
├── ArithmeticError
│ ├── FloatingPointError
│ ├── OverflowError
│ └── ZeroDivisionError
├── AssertionError
├── AttributeError
├── BufferError
├── EOFError
├── ImportError
│ └── ModuleNotFoundError
├── LookupError
│ ├── IndexError
│ └── KeyError
├── MemoryError
├── NameError
│ └── UnboundLocalError
├── OSError
│ ├── BlockingIOError
│ ├── ChildProcessError
│ ├── ConnectionError
│ │ ├── BrokenPipeError
│ │ ├── ConnectionAbortedError
│ │ ├── ConnectionRefusedError
│ │ └── ConnectionResetError
│ ├── FileExistsError
│ ├── FileNotFoundError
│ ├── InterruptedError
│ ├── IsADirectoryError
│ ├── NotADirectoryError
│ ├── PermissionError
│ ├── ProcessLookupError
│ └── TimeoutError
├── ReferenceError
├── RuntimeError
│ ├── NotImplementedError
│ └── RecursionError
├── SyntaxError
│ └── IndentationError
│ └── TabError
├── SystemError
├── TypeError
├── ValueError
│ └── UnicodeError
│ ├── UnicodeDecodeError
│ ├── UnicodeEncodeError
│ └── UnicodeTranslateError
└── Warning
├── DeprecationWarning
├── PendingDeprecationWarning
├── RuntimeWarning
├── SyntaxWarning
├── UserWarning
└── FutureWarning
| Exception | Cause | Example | Solution |
|---|
| ZeroDivisionError | Division by zero | 5 / 0 | Check divisor before operation |
| OverflowError | Result too large | Large exponential calculations | Use appropriate data types |
| FloatingPointError | Floating point operation failed | Platform-specific | Handle with try-except |
| Exception | Cause | Example | Solution |
|---|
| TypeError | Wrong type for operation | "hello" + 5 | Convert types or check types |
| AttributeError | Object has no attribute | 5.append(1) | Check object type and available methods |
| Exception | Cause | Example | Solution |
|---|
| ValueError | Correct type, wrong value | int("hello") | Validate input before conversion |
| IndexError | Index out of range | [1, 2, 3][5] | Check list length before accessing |
| KeyError | Key not found in dictionary | {'a': 1}['b'] | Use get() method or check key existence |
| Exception | Cause | Example | Solution |
|---|
| NameError | Variable not defined | Using undefined_var | Define variable before use |
| UnboundLocalError | Local variable referenced before assignment | Local var accessed before assignment | Initialize variable properly |
| ImportError | Module import failed | import nonexistent_module | Check module name and installation |
| ModuleNotFoundError | Module not found | import missing_module | Install module or check name |
| Exception | Cause | Example | Solution |
|---|
| FileNotFoundError | File doesn't exist | Opening non-existent file | Check file existence first |
| PermissionError | Access denied | Writing to read-only file | Check file permissions |
| IsADirectoryError | Expected file, got directory | Opening directory as file | Verify path is a file |
| FileExistsError | File already exists | Creating existing file with 'x' mode | Check existence or use different mode |
- Be specific: Catch specific exceptions rather than using broad
except clauses - Provide context: Include meaningful error messages and logging
- Don't ignore errors: Avoid empty
except blocks that hide problems - Use finally for cleanup: Ensure resources are properly released
- Log appropriately: Use proper logging levels and include stack traces when needed
- Fail fast: Validate inputs early and raise exceptions for invalid states
- Document exceptions: Clearly document what exceptions your functions might raise
- Test error paths: Write tests to verify exception handling works correctly
- Use context managers: Prefer
with statements for resource management - Chain exceptions: Use
raise ... from ... to preserve error context
