Public attributes with really private data

[Mark Summerfield]

On 8 May, 08:19, Peter Otten <__pete... at web.de> wrote:
> MarkSummerfieldwrote:
> > I had a quick search & didn't find anything _nice_ that produced
> > attributes with really private data, so I came up with a possible
> > solution---for Python 3.
>
> Do really you think what you suggest below is "nice"?

Well the code isn't ugly and doesn't mess with the call stack etc.

> By the way, your Attribute descriptor stores the value for all instances of
> A in the same variable...

It seems like it does, but it doesn't. The hidden_value is an instance
variable that is created every time an Attribute object is created.

>>> from Attribute import *
>>> class A:
	a = Attribute("a", 5, lambda *a: True)
	b = Attribute("b", 5, lambda *a: True)
>>> class B:
	a = Attribute("a", 5, lambda *a: True)
	b = Attribute("b", 5, lambda *a: True)
>>> a = A()
>>> b = B()
>>> a.a,a.b,b.a,b.b
(5, 5, 5, 5)
>>> a.a=1;a.b=2;b.a=3;b.b=4
>>> a.a,a.b,b.a,b.b
(1, 2, 3, 4)

--
Mark Summerfield, Qtrac Ltd, www.qtrac.eu
    C++, Python, Qt, PyQt - training and consultancy
        "Programming in Python 3" - ISBN 0137129297