setattr() oddness

[Steven D'Aprano]

On Mon, 18 Jan 2010 07:25:58 +0100, Dieter Maurer wrote:

> Lie Ryan <lie.1296 at gmail.com> writes on Sat, 16 Jan 2010 19:37:29 +1100:
>> On 01/16/10 10:10, Sean DiZazzo wrote:
>> > Interesting.  I can understand the "would take time" argument, but I
>> > don't see any legitimate use case for an attribute only accessible
>> > via getattr().  Well, at least not a pythonic use case.
>> 
>> mostly for people (ab)using attributes instead of dictionary.
> 
> Here is one use case:
> 
>  A query application. Queries are described by complex query objects.
>  For efficiency reasons, query results should be cached. For this, it is
>  not unnatural to use query objects as cache keys. Then, query objects
>  must not get changed in an uncontrolled way. I use "__setattr__" to
>  control access to the objects.


(1) Wouldn't it be more natural to store these query keys in a list or 
dictionary rather than as attributes on an object?

e.g. instead of:

cache.__setattr__('complex query object', value)

use:

cache['complex query object'] = value



(2) How does __setattr__ let you control access to the object? If a user 
wants to modify the cache, and they know the complex query object, what's 
stopping them from using __setattr__ too?




-- 
Steven