Steve D'Aprano <steve+pyt...@pearwood.info> writes:
> Why doesn't __del__ run here?
Short anser: because nothing has removed the reference to the instance.
> class Eggs(object):
> def __new__(cls):
> instance = object.__new__(cls)
> print("instance created successfully")
> return instance
> def __init__(self):
> print("self definitely exists:", self)
> raise Exception
> def __del__(self):
> print("deleting", repr(self))
This is a good example of why it helps to *never* call ‘__init__’ the
“constructor”. It isn't, because ‘__init__’ acts on an
already-constructed instance.
Hance, an exception raised from ‘__init__’ is not going to affect
whether the instance exists.
> And an example:
>
>
> py> e = Eggs()
> instance created successfully
> self definitely exists: <__main__.Eggs object at 0xb7bf21ec>
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "<stdin>", line 8, in __init__
> Exception
> py>
Right. The instance is constructed successfully (by ‘__new__’, the
constructor). It will be bound to ‘s’, creating a reference to the
instance.
The exception raised from the initialiser does not stop you from binding
the instance to a name. That binding succeeds; the reference remains.
Nothing has caused that reference to go away.
--
\ “I know that we can never get rid of religion …. But that |
`\ doesn’t mean I shouldn’t hate the lie of faith consistently and |
_o__) without apology.” —Paul Z. Myers, 2011-12-28 |
Ben Finney
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