moved imports under functions in train.py (#903)

* deleting unworking params from SumoChangeLaneParams

* deleted unworking params, sublane working in highway
:

* moved imports inside functions

* Apply suggestions from code review

* bug fixes

* bug fix

Co-authored-by: Aboudy Kreidieh <akreidieh@gmail.com>

Author: 2 people

examples/train.py

@@ -124,6 +124,9 @@ def run_model_stablebaseline(flow_params,
     stable_baselines.*
         the trained model
     """
+    from stable_baselines.common.vec_env import DummyVecEnv, SubprocVecEnv
+    from stable_baselines import PPO2
+
     if num_cpus == 1:
         constructor = env_constructor(params=flow_params, version=0)()
         # The algorithms require a vectorized environment to run
@@ -172,7 +175,12 @@ def setup_exps_rllib(flow_params,
     dict
         training configuration parameters
     """
+    from ray import tune
     from ray.tune.registry import register_env
+    try:
+        from ray.rllib.agents.agent import get_agent_class
+    except ImportError:
+        from ray.rllib.agents.registry import get_agent_class
 
     horizon = flow_params['env'].horizon
 
@@ -404,6 +412,9 @@ def train_h_baselines(flow_params, args, multiagent):
 
 def train_stable_baselines(submodule, flags):
     """Train policies using the PPO algorithm in stable-baselines."""
+    from stable_baselines.common.vec_env import DummyVecEnv
+    from stable_baselines import PPO2
+
     flow_params = submodule.flow_params
     # Path to the saved files
     exp_tag = flow_params['exp_tag']