OO in Python? ^^

[Paul Boddie]

Steven D'Aprano wrote:
> I look at it this way: as the class designer, I have ZERO idea what
> attributes and methods of my class will be just the perfect thing to solve
> somebody's problem, so it is rude of me to lock them up as private --
> especially since they *will* find a way to hack my class and access my
> private attributes and methods anyway.

Actually, one good aspect of "attribute privacy" is the lowered risk of
instance attribute name clashes. When subclassing from some partly
abstract class in order to specialise its behaviour
(sgmllib.SGMLParser, for example), one has to make sure that one
doesn't reuse some instance attribute name by accident - doing so could
potentially cause behavioural issues in the superclass's mechanisms.
That said, Python does at least let you look at which attributes are
already defined in an instance due to the lack of privacy, so it does
offer some kind of solution to that problem. Moreover, Python also lets
you define double-underscore attribute names which behave give instance
attributes privacy in all respects, being invisible to users of the
instances concerned, accessible only within methods belonging to the
defining class, and safely overloadable in subclasses without incurring
conflicts.

Generally, I'm in agreement with you, though: private, protected and
final are all things which provide easy distractions from more serious
and demanding issues. They can quite often prove to be "the bikeshed"
in system design and implementation.

Paul