werkzeug.utils.cached_property

A property that is only evaluated once. Subsequent access returns the cached value. Setting the property sets the cached value. Deleting the property clears the cached value, accessing it again will evaluate it again.

class Example:
    @cached_property
    def value(self):
        # calculate something important here
        return 42

e = Example()
e.value  # evaluates
e.value  # uses cache
e.value = 16  # sets cache
del e.value  # clears cache

The class must have a __dict__ for this to work.