On 18 February 2002, Kevin Jacobs said:
> My recent post on __slots__ not being picklable (and the resounding lack of
> response to it)
Certainly caught my attention, but I had nothing to add.
> 1) Should class instances explicitly/directly know all of their attributes?
I'm not sure you're asking the right question. If you're concerned with
introspection, shouldn't the question be: "Should arbitrary code be able
to find out the set of attributes associated with a given object?" The
Pythonic answer is clearly yes. And if "attribute" means "something
that follows a dot", then you can do this using dir(). Unfortunately,
the expansion of dir() to include methods means it's no longer very
useful for getting just instance attributes, whether they're in a
__dict__ or some other method.
So the obvious answer is to use vars(), which works on classic classes
and __slots__-less new-style classes. (I think vars(x) is just a more
sociable way to spell x.__dict__.) But it bombs on classes with
__slots__:
>>> class C(object):
... __slots__ = ['a', 'b']
...
>>> c = C()
>>> vars(c)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: vars() argument must have __dict__ attribute
Uh-oh. This is a problem.
> 3) Should __slots__ be immutable?
Yes, definitely. Clearly __slots__ is a property of the type (class),
not of the instance, and once the class is defined, that's it. (Or that
should be it.) It looks as though you can modify __slots__, but it has
no effect; that's mildly bogus.
> 4) Should __slots__ be flat?
Hmmmm... probably. That's certainly consistent with "... once the class
is defined, that's it".
Greg
--
Greg Ward - geek-at-large gward@python.net
http://starship.python.net/~gward/
If you and a friend are being chased by a lion, it is not necessary to
outrun the lion. It is only necessary to outrun your friend.
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