daniel.dittmar at sap.corp
Tue Jan 18 19:05:37 CET 2005
Kevin Smith wrote:
> 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?
If you use the old-fashioned __getattr__ method instead of properties.
__getattr__ gets called only if the value can't be found in the instance
def __getattr__ (self, attrname):
method = getattr (self, 'calculate_' + attrname)
raise AttributeError, attrname
value = method ()
setattr (self, attrname, value)
And probably also through metaclasses. And decorators.
More information about the Python-list