> >>>>> "GvR" == Guido van Rossum <guido@python.org> writes:
>
> GvR> Now I have a choice to make. If the class has an __init__,
> GvR> should I clear the flag only after __init__ succeeds? This
> GvR> means that if __init__ raises an exception, __del__ is never
> GvR> called. This is an incompatibility. It's possible that
> GvR> someone has written code that relies on __del__ being called
> GvR> even when __init__ fails halfway, and then their code would
> GvR> break.
[Barry]
> It reminds me of the separation between object allocation and
> initialization in ObjC.
Is that good or bad?
> GvR> But it is just as likely that calling __del__ on a partially
> GvR> uninitialized object is a bad mistake, and I am doing all
> GvR> these cases a favor by not calling __del__ when __init__
> GvR> failed!
>
> GvR> Any opinions? If nobody speaks up, I'll make the change.
>
> I think you should set the flag right before you call __init__(),
> i.e. after (nearly all) the C level initialization has occurred.
> Here's why: your "favor" can easily be accomplished by Python
> constructs in the __init__():
>
> class MyBogo:
> def __init__(self):
> self.get_delified = 0
> do_sumtin_exceptional()
> self.get_delified = 1
>
> def __del__(self):
> if self.get_delified:
> ah_sweet_release()
But the other behavior (call __del__ even when __init__ fails) can
also easily be accomplished in Python:
class C:
def __init__(self):
try:
...stuff that may fail...
except:
self.__del__()
raise
def __del__(self):
...cleanup...
I believe that in almost all cases the programmer would be happier if
__del__ wasn't called when their __init__ fails. This makes it easier
to write a __del__ that can assume that all the object's fields have
been properly initialized.
In my code, typically when __init__ fails, this is a symptom of a
really bad bug (e.g. I just renamed one of __init__'s arguments and
forgot to fix all references), and I don't care much about cleanup
behavior.
--Guido van Rossum (home page: http://www.python.org/~guido/)
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