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

Steven Bethard steven.bethard at gmail.com
Mon Dec 12 05:53:26 CET 2005

On 12/11/05, Guido van Rossum <guido at python.org> wrote:

On 12/11/05, Nick Coghlan <ncoghlan at gmail.com> wrote: > Keeping it for Py3K would be fine, if the mechanism was changed so that it > actually worked right. That is, the mechanics would be such that any two > concurrently existing classes would be guaranteed to mangle the names of their > private variables differently - simply using the class name (as now) doesn't > guarantee that when inheriting from a class in a different module and reusing > the name.

I know about the fear of accidental reuse of class names, but I don't find it a compelling argument.

FWIW, I know I currently have a number of classes that are potentially hazardous in this way. Each of these classes is basically a substitute class for a third-party API that I have to code to. The API is missing a number of convenience methods, and the most straightforward way to introduce these methods[1] is to create a subclass of the appropriate class. Since they are in a different module, it seems perfectly normal for me to give them the same name since for all external modules, they should look the same as the original API (but with the added methods). So I have a number of classes that look something like:

class Document(_cdm.Document): ... # add convenience methods here ...

I don't use double-underscore name mangling, but if I did, it would clearly fail in this case.

[1] I've concluded this after a variety of refactorings. But perhaps there is a better way...

Also, I like the current, well-defined mangling algorithm; it means that when I'm in the debugger I can manually mangle or unmangle names as required.

Why couldn't the name mangling do something like:

'_%s_%s__%s' % (cls.__module__, cls.__name__, attrname)

This would still allow manual mangling/unmangling, and it seems like it would cover most of the same-name different module concerns...

STeVe

You can wordify anything if you just verb it. --- Bucky Katt, Get Fuzzy

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