class reify(object):

    """ Put the result of a method which uses this (non-data)
    descriptor decorator in the instance dict after the first call,
    effectively replacing the decorator with an instance variable."""

    def __init__(self, wrapped):
        self.wrapped = wrapped

    def __get__(self, inst, objtype=None):
        if inst is None:
            return self
        val = self.wrapped(inst)
        setattr(inst, self.wrapped.__name__, val)
        return val