Clean way to not get object back from instantiation attempt gone bad

[olsongt at verizon.net]

tobiah wrote:
> Suppose I do:
>
>
> myfoo = Foo('grapes', 'oranges')
>
> And in the __init__() of Foo, there is
> a real problem with the consumption of fruit.
> Is there a clean way to ensure that myfoo
> will be None after the call?  Would the
> __init__() just do del(self), or is there
> a better way to think about this?
>
> Thanks,
>
> Toby

As others have said, just raise an exception.  You can hide
instantiation inside a factory function to simulate the behaviour
you're specifically talking about:

class Foo:
    def __init__(self, *args):
        for arg in args:
            if is_fruit(arg):
                 raise RuntimeError("I don't like fruit")


def FooFactory(*args):
    try:
        return Foo(*args)
    except RuntimeError:
        return None

-Grant