On Wed, Feb 1, 2012 at 9:13 AM, Hans Mulder <hansmu@xs4all.nl> wrote:
On 30/01/12 00:30:14, Steven D'Aprano wrote:
Mark Shannon wrote:
Antoine Pitrou wrote:
[......]
Antoine is right. It is a reorganisation of the dict, plus a couple of changes to typeobject.c and object.c to ensure that instance dictionaries do indeed share keys arrays.
I don't quite follow how that could work.
If I have this:
class C: pass
a = C() b = C()
a.spam = 1 b.ham = 2
how can a.__dict__ and b.__dict__ share key arrays? I've tried reading the source, but I'm afraid I don't understand it well enough to make sense of it.
They can't.
But then, your class is atypical. Usually, classes initialize all the attributes of their instances in the __init__ method, perhaps like so:
class D: def __init__(self, ham=None, spam=None): self.ham = ham self.spam = spam
As long as you follow the common practice of not adding any attributes after the object has been initialized, your instances can share their keys array. Mark's patch will do that.
You'll still be allowed to have different attributes per instance, but if you do that, then the patch doesn't buy you much.
Hey, I like this! It's a subtle encouragement for developers to initialize all their instance variables in their __init__ or __new__ method, with a (modest) performance improvement for a carrot. (Though I have to admit I have no idea how you do it. Wouldn't the set of dict keys be different while __init__ is in the middle of setting the instance variables?) Another question: a common pattern is to use (immutable) class variables as default values for instance variables, and only set the instance variables once they need to be different. Does such a class benefit from your improvement?
-- HansM
-- --Guido van Rossum (python.org/~guido)