Ch 1 covers exception handling — the mechanism to deal with runtime errors gracefully. Learn try-except blocks, finally clause, raising exceptions, and built-in exception types.
Errors: Syntax errors (invalid code — caught before execution) vs Exceptions (runtime errors). try-except: try: block with risky code; except ExceptionType: handling code. Can catch specific exceptions: except ValueError: or multiple: except (ValueError, TypeError):. Generic: except: or except Exception as e:. else clause: runs if NO exception occurred. finally: ALWAYS runs — for cleanup (closing files, connections). Nesting: try inside try for multi-level handling.
Common exceptions: ValueError (wrong value: int("abc")), TypeError (wrong type: "2" + 2), ZeroDivisionError (5/0), IndexError (list[100]), KeyError (dict["missing"]), FileNotFoundError, NameError (undefined variable), AttributeError (invalid method), ImportError, OverflowError. raise: explicitly trigger an exception: raise ValueError("Age must be positive"). Custom exceptions: class InvalidAgeError(Exception): pass — then raise InvalidAgeError("message"). Best practices: catch specific exceptions, don't use bare except:, use finally for cleanup, log errors.
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Both can prevent crashes, but there's a key philosophy difference. Python follows EAFP (Easier to Ask Forgiveness than Permission): try the operation, handle the exception if it fails. This is cleaner when errors are rare. if-else follows LBYL (Look Before You Leap): check every condition before acting. EAFP advantages: (1) Handles unexpected errors (you can't predict every failure mode). (2) Cleaner code when multiple things can go wrong. (3) Atomic operations — file access may fail between check and use. Use both as appropriate, but try-except is idiomatic Python for error handling.
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