# \[RLlib\] Multiagent with one pre-trained policy (vs another adversarial one)

**URL:** <https://discuss.ray.io/t/rllib-multiagent-with-one-pre-trained-policy-vs-another-adversarial-one/428>\
**Category:** RLlib\
**Created:** [January 13, 2021, 12:13pm UTC](https://discuss.ray.io/t/rllib-multiagent-with-one-pre-trained-policy-vs-another-adversarial-one/428 "2021-01-13T12:13:24Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![Rory](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/rory/32/688_2.png) [@Rory](https://discuss.ray.io/u/Rory)\
**Post date:** [April 20, 2021, 4:16pm UTC](https://discuss.ray.io/t/rllib-multiagent-with-one-pre-trained-policy-vs-another-adversarial-one/428/3 "2021-04-20T16:16:27Z")

</div>

What is the best way to load a specific policy’s weights from a checkpoint file to the be used as another trainers policy? I’d like to use a pre-trained model to evaluate the currently training one against in a marl setting.

Doing something like this doesn’t work for me:

```
        loader = get_trainer_class(algo)(env="yaniv", config=config)
        loader.load_checkpoint(checkpoint_path)
        policy = loader.get_policy("policy_1").get_weights()
        self.trainer.set_weights({
            "eval_policy": policy
        })

```

I think this is because it makes a new trainer with all the workers and what not, where as I just want the policy, and gives the following error:

```
(pid=56641) File "/home/jippo/Code/yaniv/yaniv-rl/yaniv_rl/utils/rllib/trainer.py", line 18, in setup
(pid=56641) loader.load_checkpoint(checkpoint_path)
(pid=56641) File "/home/jippo/.conda/envs/yaniv-torch/lib/python3.7/site-packages/ray/rllib/agents/trainer.py", line 755, in load_checkpoint
(pid=56641) self. __setstate__ (extra_data)
(pid=56641) File "/home/jippo/.conda/envs/yaniv-torch/lib/python3.7/site-packages/ray/rllib/agents/trainer_template.py", line 191, in __setstate__
(pid=56641) Trainer. __setstate__ (self, state)
(pid=56641) File "/home/jippo/.conda/envs/yaniv-torch/lib/python3.7/site-packages/ray/rllib/agents/trainer.py", line 1321, in __setstate__
(pid=56641) self.workers.local_worker().restore(state["worker"])
(pid=56641) File "/home/jippo/.conda/envs/yaniv-torch/lib/python3.7/site-packages/ray/rllib/evaluation/rollout_worker.py", line 1059, in restore
(pid=56641) self.sync_filters(objs["filters"])
(pid=56641) File "/home/jippo/.conda/envs/yaniv-torch/lib/python3.7/site-packages/ray/rllib/evaluation/rollout_worker.py", line 1026, in sync_filters
(pid=56641) assert all(k in new_filters for k in self.filters)
(pid=56641) AssertionError
```

---

_[View the full topic](https://discuss.ray.io/t/rllib-multiagent-with-one-pre-trained-policy-vs-another-adversarial-one/428)._