Error Handling in Python

Learn how errors work in Python: runtime errors, exception types, try-except-finally, raising exceptions, custom exception classes, propagation, and stack traces.

Introduction to Errors

Errors (exceptions) occur when Python cannot execute code as expected. If not handled, the program stops immediately.

1. What is an Exception?

Runtime failure.

Common Exception Types

Python provides many built-in exception classes.

1. NameError

Undefined variable.

2. TypeError

Invalid operation on type.

3. ValueError

Invalid value.

4. ZeroDivisionError

Division by zero.

5. IndexError

Invalid list index.

try / except

try-except allows handling exceptions safely without crashing the program.

1. Basic try-except

Catch errors.

2. Access Exception Object

Capture error details.

3. Multiple except Blocks

Handle different errors differently.

finally Block

finally always runs whether exception occurs or not.

1. finally Execution

Cleanup code.

Raising Exceptions

raise allows manually triggering exceptions.

1. raise ValueError

Manual failure.

Custom Exception Classes

Custom exceptions improve clarity and allow domain-specific error handling.

1. Creating Custom Exception

Extend Exception.

Exception Propagation

Exceptions bubble up the call stack until handled.

1. Bubbling Example

Unhandled error travels upward.

Stack Trace & Traceback

Python prints a traceback when an exception is not handled.

1. What is a Traceback?

Execution history.

2. Using traceback Module

Programmatic stack access.