@singleton('target_encoder')
def _get_target_encoder(self):
    target_encoder = copy.deepcopy(self.online_encoder)
    set_requires_grad(target_encoder, False)
    return target_encoder
@singleton('target_encoder')
def _get_target_encoder(self):
    target_encoder = copy.deepcopy(self.online_encoder)
    set_requires_grad(target_encoder, False)
    return target_encoder