code: def default_behavior_policy(
      networks: dqn_networks.DQNNetworks, epsilon: Epsilon
  ) -> EpsilonPolicy:
      """A policy with a fixed-epsilon epsilon-greedy exploration.
  
      DEPRECATED: use behavior_policy instead.
      Args:
        networks: DQN networks
        epsilon: sampling parameter that overrides the one in EpsilonPolicy
      Returns:
        epsilon-greedy behavior policy with fixed epsilon
      """
      # TODO(lukstafi): remove this function and migrate its users.
  
      def apply_and_sample(
          params: networks_lib.Params,
          key: networks_lib.PRNGKey,
          observation: networks_lib.Observation,
          _: Epsilon,
      ) -> networks_lib.Action:
          # TODO(b/161332815): Make JAX Actor work with batched or unbatched inputs.
          observation = utils.add_batch_dim(observation)
          action_values = networks.policy_network.apply(
              params, observation, is_training=False
          )
          action_values = utils.squeeze_batch_dim(action_values)
          return networks.sample_fn(action_values, key, epsilon)
  
      return apply_and_sample
  
file_path: acme/acme/agents/jax/dqn/actor.py
imports: from typing import Callable, Sequence
  from acme.agents.jax import actor_core
  from acme.agents.jax.dqn import networks
  from acme.jax import networks
  from acme.jax import utils
  import chex
  import jax
  import jax.numpy
label_desc: Use image node_id 3 for calling a global function with example usage: default_behavior_policy(networks, epsilon) and returns: apply_and_sample, networks