On Sun, 31 Dec 2006 19:48:55 -0800, Tom Plunket wrote: > Steven D'Aprano wrote: > >> What does the author of the original class know about *my* needs and >> requirements? > > The only thing that the original class author might know is that mucking > with data marked private may well cause problems, and hiding it > therefore prevents those problems.
Sure. That's the risk I take when I muck about with somebody else's private attributes. >> It may turn out that accessing his "private" attributes is exactly what >> I need to solve my problem. > > It may also turn out that you /think/ that's what you need to do, but > actually need to do something different. And how is that different from *any* programming task? I might think I need a binary tree, when all I really need is a simple list. An error is an error, whether it is with a public API or a private one. > E.g. it may well be possible to access the bytes on the disk that holds > your database directly, and that may be "easier" than going through the > db API, but doing so may also be highly prone to error. No, I doubt it is "easier" -- but if I'm programming a database recovery tool that fixes corrupted databases because the db vendor's supplied tool is broken or non-existent, that might be exactly what I need to do. >> I'm with the Python philosophy on this one: post all the "Don't Touch >> This" warning signs you like, but if somebody really wants to access my >> private attributes, to do something I never even imagined, they should >> be allowed to. > > You are allowed to. Have you been following the thread? Your answer's > been mentioned several times. Yes, mostly by me. Do try to keep up. > At the same time, you should ponder very > carefully the reasons why the original author deemed it important to > make those attributes private in the first place. In my experience, it is mostly because they come from bondage-and-domination languages where it is expected that everything is private except for a small, carefully chosen public API, rather than from languages like Python that encourages openness and a philosophy of "we're all adults here". I wonder how many double-underscore "private" attributes are used in the Python standard library? That should give you an idea of "best practice" use of private attributes in Python. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
