One-Shot Property?

[Kevin Smith]

I have many cases in my code where I use a property for calculating a 
value on-demand.  Quite a few of these only need to be called once.  
After that the value is always the same.  In these properties, I set a 
variable in the instance as a cached value and return that value on 
subsequent calls.  It would be nice if there was a descriptor that would 
do this automatically.  Actually, what would be really nice is if I 
could replace the property altogether and put the calculated value in 
its place after the first call, but the property itself prevents me from 
doing that.  Is this possible?

-- 
Kevin Smith
Kevin.Smith at sas.com