Question

I have a few computationally expensive properties on some classes. These properties do not change as long as the mutable/underlying attributes do not change. Is there a way to store the expensive property, and only re-calculate it if a change has been made?

Answer 1

You can test for the other variables in your property method and use them as part of a cache key:

class CachedProperties(object):
    @property
    def expensiveValue(self):
        cacheKey = (self.var1, self.var2)
        if cacheKey in self._expensiveValueCache:
            return self._expensiveValueCache[cacheKey]

        # No cached value available, calculate it now
        res = self._expensiveValueCache[cacheKey] = calculation(self.var1, self.var2)
        return res

Now you defer calculation until you actually need the expensive value and var1 or var2 have changed.