Exception Handling Patterns

Effective exception handling distinguishes robust Python applications from fragile ones. It goes beyond simply suppressing errors; it involves communicating failure states clearly and ensuring system stability.

Catching Specific Exceptions

Avoid bare except: clauses. They catch everything, including system exit signals and keyboard interrupts, making debugging a nightmare. Always specify the exception type.

Exception Chaining

When you catch an exception and raise a new one (perhaps to wrap a low-level error in a high-level application error), you risk losing the original traceback. Python 3 solves this with raise ... from ....

This attaches the original exception (`e`) to the new one as the `__cause__` attribute, aiding debugging.

The else and finally Blocks

The try-except statement supports two optional blocks:

• else: Runs only if the try block did not raise an exception. It's better than putting code inside the try block because it avoids accidentally catching exceptions you didn't intend to handle.
• finally: Runs always, whether an exception occurred or not. Use it for cleanup (closing files, releasing locks).