[Python-Dev] Deprecate __ private (was Re: PEP 8 updates/clarifications) (original) (raw)

Jim Fulton jim at zope.com
Sun Dec 11 23:57:58 CET 2005

Ian Bicking wrote:

Jim Fulton wrote: ...

Also decide whether your attributes should be private or not. The difference between private and non-public is that the former will never be useful for a derived class, while the latter might be. Yes, you should design your classes with inheritence in mind!

Private attributes should have two leading underscores, no trailing underscores. This conflicts with a previous suggestion "Generally, double leading underscores should be used only to avoid name conflicts with attributes in classes designed to be subclassed." Or perhaps "private attributes" needs to be better explained.

While, on some level, private variables seem attractive, I think that experience (for everyone I know) has shown them to be an attractive nuisance. I recommend discouraging them. I really really hate double underscores, but I thought I'd let some other people suggest stronger language first. I prefer explicit name mangling for those cases where people justifiably use double underscores _now, e.g., self.MyPackagevariable instead of self.variable, which I think you also suggest below. Since it's all name mangling anyway, at least explicit is better than implicit, especially when it's something one could argue should look a little ugly. Perhaps all the non-public/private language should be switched to just "private" (one underscore) and "hidden from subclasses" (double underscore). I don't like calling _ private at all, because it's not what people coming from other languages think of as private.

Can we officially mark __private as a mistake. Perhaps:

Jim

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