Problems translating map file layers to mapscript

[Damon Butler]

[...]
>> They can be made transparent by supplying negative numbers for the R, G,
>> and B values.
>>
>> c.label.backgroundcolor = mapscript.colorObj(-1, -1, -1)
>> c.label.outlinecolor = mapscript.colorObj(-1, -1, -1)
> 
> Never done must this be! Proper usage is
> 
>     c.label.backgroundcolor.setRGB(-1, -1, -1)
>     c.label.outlinecolor.setRGB(-1, -1, -1)
> 
> Otherwise the previously defined colors will be dereferenced improperly 
> and never cleaned up by Python's garbage collector. Anyhow, these 
> attributes begin with default values (-1, -1, -1), so no need to alter 
> them if you want the no-background default.

I (we, actually) tried your syntax, but neither the backgroundcolor nor 
the outlinecolor attributes on the label object are color objects, and 
so attempting to call the setRGB method on them fails with an 
AttributeError. According to the mapscript API, and introspection of a 
mapscript-parsed map file in a Python interpreter, those attributes must 
be set with mapscript color objects. Hence the code I previously listed.

I should note that the layer in question is being generated entirely 
from scratch with mapscript. It is not being modified from a layer that 
has been read in from a map file. We have learned that this means we 
have to set all kinds of default values that otherwise appear to be 
assumed. Having no background, for example, is not the default behavior 
for a layer generated entirely using mapscript commands. (It is, in 
fact, a solid black rectangle.)

Your suggestion to specify basic values for our layers in a map file and 
then merely modify them via mapscript commands is an excellent one, 
however, and definitely would simplify what we're trying to do. For 
workflow considerations, we hadn't considered it, let alone thought it 
possible.

Thanks!
--Damon