def __init__(self, *args, **kwargs):
    super(Feature, self).__init__(*args, **kwargs)
    for (prop_name, prop) in self.properties().iteritems():
        old_val = getattr(self, prop_name, None)
        setattr(self, ('_old_' + prop_name), old_val)
def __init__(self, *args, **kwargs):
    super(Feature, self).__init__(*args, **kwargs)
    for (prop_name, prop) in self.properties().iteritems():
        old_val = getattr(self, prop_name, None)
        setattr(self, ('_old_' + prop_name), old_val)