[Tutor] calling setters of superclasses

[Matt Gregory]

On 12/18/2010 2:06 AM, Peter Otten wrote:
> I don't think /how/ you are trying it is stupid though I'm not so sure about
> /what/ .

Thank you all for very helpful suggestions.  It took me a while to chew 
on this before I could respond.  I learned a lot about descriptors and 
their interactions with properties that I hadn't fully understood before.

Peter and Alan's advice to create a check method that is overridden in 
subclasses makes sense in order to avoid the naming conflicts.  And I 
also like Hugo's idea of applying separate descriptor classes to handle 
the constraints introduced.  That seems to be a flexible way of doing 
things.

As far as the /what/, my example given was obviously contrived.  I'm 
really trying to create classes for 2D envelopes that describe the 
bounding extent of spatial data.  I have both Envelope and 
RasterEnvelope classes - the former being just a bounding box around any 
spatial data, the latter additionally specifying a raster cell size and 
being able to discern rows, columns, etc.

I had been using the setter to do bounds checking on the Envelope class 
(e.g. make sure x_min isn't bigger than x_max, etc. and rolling back 
changes if so).  For the RasterEnvelope class, I first wanted to call 
the Envelope bounds checking and then to adjust rows/columns if a bigger 
extent was requested.  But you've successfully scared me away from using 
properties (in a hierarchical way at least) and I've been able to get 
what I need by just defining __setattr__ in both classes.  Whether I did 
that correctly is a story for another thread ...

matt