Python course / Working Python

Errors and exceptions

Read a traceback, catch the failure you expected, and raise one a caller can act on. Real input breaks programs, and how yours fails is part of how well it is written.

• tracebacks
• try and except
• else and finally
• raising
• your own exceptions
• where to catch
• cleanup
• retries

Start this module

Runs in your browser. Start straight away; create an account when you want your progress kept.

def portion(total, people):
    if people <= 0:
        raise ValueError(f"people must be positive, got {people}")
    return total / people


for people in [4, 0]:
    try:
        print("each gets", portion(10, people))
    except ValueError as failure:
        print("refused:", failure)

each gets 2.5
refused: people must be positive, got 0