[SAGA-RG] SAGA attributes as Python dictionaries?

[Ceriel Jacobs]

Andre Merzky wrote:
> Quoting [Mathijs den Burger] (Nov 04 2009):
>> Hi all,
...
>> 2. Removing SAGA attributes is permanent (AFAIK when talking to Ceriel),
>> while a deleted dict item can be re-added latter
> 
> Not sure I undestand.  the following should be valid:
> 
>   if ( ! advert.attribute_exists ("foo") )
>   {
>     advert.set_attribute ("foo", "bar");
>   }
> 
>   assert (advert.attribute_exists ("foo"), true);
> 
>   advert.remove_attribute ("foo");
> 
>   assert (advert.attribute_exists ("foo"), false);
> 
>   advert.set_attribute ("foo", "bar");
> 
>   assert (advert.attribute_exists ("foo"), true);

Actually, I have an issue with this: I don't think this is valid.

Here is why, and it all depends on what the Saga specs mean
by "exists".
The notes at set_attribute say, a.o.: "the attribute is created,
if it does not exist" and also "only some SAGA objects allow to
create new attributes - others allow only access to predefined
attributes.  If a non-existing attribute is queried on such
objects, a 'DoesNotExist' exception is raised". I take this to mean
that ALL attributes mentioned in the SAGA specs DO exist, even
if they don't have a value.
Now, remove_attribute has as PostCond: "the attribute is not available anymore."
I assume this means: "the attribute does not exist anymore", what else would
it mean?
So, attribute_exists() returns false on a removed attribute, but then
a call to set_attribute() gives a "DoesNotExist".

 From Mathijs, I understand that the C++ implementation has a different
take on what "exists" means. I may even like that interpretation better,
but I don't think it is supported by the current Saga specs.

Cheers,		Ceriel