Python Tutorial: Error Handling
Things go wrong. Handle it gracefully with try, except, else, finally, and custom exceptions.
Every program encounters errors
Files are missing. Networks are down. Users type nonsense. Dividing by zero. Index out of range.
Python's exception system lets you catch errors and respond intelligently — instead of crashing. Twelve steps.
What you'll learn in this Python error handling tutorial
This interactive Python tutorial has 9 hands-on exercises. Estimated time: 20 minutes.
- Things go wrong — handle it — Your programs will encounter errors. Files that don't exist. Networks that go down. Users who type nonsense when asked f…
- try/except — catch the crash — Wrap the risky code in `try`. If an exception happens, Python jumps to `except` instead of crashing.
- Multiple except blocks — Different errors need different responses. Add multiple `except` blocks for each:
- else — the 'it worked!' block — `else` on a try/except runs only if NO exception was raised:
- finally — always runs — `finally` runs no matter what — exception or not. Perfect for cleanup:
- raise — throw your own exception — You can raise exceptions yourself when you detect invalid input:
- Custom exceptions — Built-in exceptions (ValueError, TypeError, etc.) are generic. For your own code, create specific exception types:
- raise from — chain exceptions — `raise X from Y` chains exceptions — the new exception knows it was caused by the original:
- Build a data validator — Final challenge — no starter code.
Python Error Handling concepts covered
- Every program encounters errors