On Sat, Feb 22, 2014 at 12:55 PM, Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:
Steven D'Aprano wrote:
result = computation( int(arg) except ValueError: abort("Invalid int") )
Actually, not quite so nice as I first thought, since you're relying on the side-effects of abort() rather than returning a value.
Yeah, while I was writing that I wondered whether you should be allowed to write
int(arg) except ValueError: raise UserError("Invalid int")
That looks heretical, because 'raise' can't in any way be interpreted as a value-returning expression. But you can achieve the same result using a function that always raises and exception, so forbidding it on those grounds would be pointless.
def throw(exc): raise exc int(arg) except ValueError: throw(UserError("Invalid int")) Tiny helper function and then it doesn't need any special syntax. It's not so much that PEP 463 forbids this, as that it doesn't explicitly permit it. The 'default' part of the syntax is an expression, raise is not an expression, ergo it's not permitted. But if you think this is sufficiently common (translate an exception on the way through), show some code and justify its addition - or just write up a separate proposal for "raise X" to become an expression, same as "yield X" is. ChrisA