empty classes as c structs?

[Alex Martelli]

Steven Bethard <steven.bethard at gmail.com> wrote:

> Seems pretty reasonable -- the only thing I worry about is that 
> classmethods and other attributes (e.g. properties) that are accessible
> from instances can lead to subtle bugs when a user accidentally 
> initializes a Bunch object with the attributes of the same name, e.g.:
> 
>      b = Bunch(getDict=1)
> 
> where
> 
>      b.getDict()
> 
> now fails with something like "TypeError: 'int' object is not callable".

Well, that's the problem with confusing items and attributes in the
first place, of course -- which IS Bunch's purpose;-)

>   (For another discussion about this problem, see [1]).
> 
> I don't know what the right solution is here...  I wonder if I should
> write a classmethod-style descriptor that disallows the calling of a 
> function from an instance?  Or maybe I should just document that the 
> classmethods should only be called from the class?  Hmm...

Another approach is to add a few "reserved words" to the ones Python
itself would reject in the initialization.  Just you cannot do:

    b = Bunch(continue=23)

you may choose to forbid using getDict=42 - if you do that you probably
want to forbid any magicname too, since e.g.

    b = Bunch(__dict__=99)

can't work ``right'' no matter what, while setting e.g. __deepcopy__
similarly might confuse any copy.deepcopy(b), etc, etc.

> How do you feel about getDict and setDict also being classmethods?

Uh?  I want to get or set the dict of a specific instance -- not those
of the whole class.  How would you design them as classmethods...?


Alex