On 28/06/2011 13:56, Michael Foord wrote:
On 28/06/2011 13:31, Nick Coghlan wrote:
On Tue, Jun 28, 2011 at 8:54 PM, Michael Foord
<fuzzy...@voidspace.org.uk> wrote:
The problem with "data attributes" is that it doesn't mean
*anything*, which
I suppose is useful for invented terminology, but it means it
doesn't convey
anything precise to those who haven't heard the term before. If it
becomes
widely used then that changes I guess. I'd still normally just use
"attributes" though...
In this context, precision is an illusion. There is *no* precise
terminology,
"instance members" is precise, (whether or not an attribute is fetched
"from the instance" is one thing that is clear in the python data
model - there are just lots of other ways of fetching attributes too).
"instance members" just doesn't cover all the cases where you may want
to group attributes together though.
However, providing "__getattr__" and "__getattribute__" is not the
common case and even properties are *usually* backed by a real
instance attribute. So "instance attributes" as opposed to other types
of attributes is *often* a useful distinction.
I don't think "data attributes" is clear or precise.
Although to be fair "data attributes" mirrors the terminology for
descriptors where we have "data descriptors" (which have both __set__
and __get__) and "non data descriptors" (__get__ only). Unfortunately
there are also non-non-data decriptors too (only __set__ and / or
__delete__) so that terminology is at least slightly confusing /
imprecise [1]... There was a genuine Python "bug" caused by that
confusion at one point (unfortunately I forget what it was).
All the best,
Michael
[1] From: http://users.rcn.com/python/download/Descriptor.htm
If an object defines both __get__ and __set__, it is considered a
data descriptor. Descriptors that only define __get__ are called
non-data descriptors (they are typically used for methods but other uses
are possible).
Is a property a data attribute (well it depends how it is implemented
and what it does), is a staticmethod a data attribute (no - but then
Tres' question - it isn't a normal method either so if you define data
attribute to mean "all non method attributes" then its potentially an
open question).
All the best,
Michael Foord
not only because Python blurs the boundaries by design in
many respects (callable or not, method or not, attribute or not, etc),
but also because *people* use the same words to mean slightly
different things.
The best we can hope for is to encourage the right way of thinking
about the situation, and in that regard you have the complete set of
attributes accessible via an object (i.e. via __getattribute__), some
of which are callables (and may or may not act like instance methods)
and the remainder of which are data attributes (some of which may
incidentally be callable, even if they aren't used that way). How a
*particular* attribute is classified is not an inherent property of
the attribute, but also an artifact of the way it is used by the
application.
Cheers,
Nick.
--
http://www.voidspace.org.uk/
May you do good and not evil
May you find forgiveness for yourself and forgive others
May you share freely, never taking more than you give.
-- the sqlite blessing http://www.sqlite.org/different.html
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