Always catch specific exceptions, never bare except. Define custom exception hierarchies so callers can catch at different granularities. Use raise X from Y to chain exceptions and preserve the original traceback. raise X from None suppresses the original to present a clean error to callers.

Bare except: catches SystemExit and KeyboardInterrupt, masking serious problems. Custom exception hierarchies let you catch a broad base class for all domain errors or a specific subclass for a particular failure. The else block in try/except runs only when no exception was raised — better than putting success code at the end of try where it could be accidentally caught. The finally block always runs, even if a return is hit inside try. raise X from err sets __cause__ on the new exception and shows both in the traceback; raise X from None suppresses the original for clean external errors.