On Tue, 27 Nov 2012 15:59:38 -0800, lars van gemerden wrote:
> Hi,
>
> I get a very strange result when using deepcopy. The following code:
>
> def __deepcopy__(self, memo):
> independent = self.independent()
> if independent is self:
> out = type(self)()
> out.__dict__ = copy.deepcopy(self.__dict__, memo)
> print self.__dict__
> print out.__dict__ #strange result
> return out
> else:
> return copy.deepcopy(independent, memo).find(self.id).take()
>
> prints different results for self.__dict__ and out.__dict__:
What makes you think that this is a strange result? What result are you
expecting?
> {'_active_': False, 'init': {}, '_id_': 0, '_items_':
> [<flow.library.collector object at 0x03893910>], '_name_': 'main'}
> {'_active_': False, 'init': {}, '_id_': 0}
>
> Two items are missing in the copy. Maybe i am missing something obvious,
> but i cannot figure out how this could happen.
>
> Can anyone tell me how this is possible?
The most obvious guess is that the memo dict already contains _items_ and
_names_, and so they get skipped.
Please ensure your sample code can be run. You should create the simplest
example of stand-alone code that other people can run. See more
information here:
http://sscce.org/
By the way, is it just me or is the documentation for deepcopy seriously
lacking? http://docs.python.org/3/library/copy.html
There's no mention of the additional arguments memo and _nil, and while
the docs say to pass the memo dictionary to __deepcopy__ it doesn't
document any restrictions on this memo, how to initialise it, or under
what circumstances you would pass anything but an empty dict.
--
Steven
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