Question

How do I elegantly implement the "Samurai principle" (return victorious, or not at all) on my functions?

return <value> if <bool> else raise <exception>

Answer 1

Inline/ternary if is an expression, not a statement. Your attempt means “if bool, return value, else return the result of raise expression” – which is nonsense of course, because raise exception is itself a statement not an expression.

There’s no way to do this inline, and you shouldn’t want to. Do it explicitly:

if not bool:
    raise MyException
return value