[rllib] bug fix: merging --config params with params.pkl (ray-project…

…#4336)

python/ray/rllib/rollout.py

@@ -12,6 +12,7 @@
 import gym
 import ray
 from ray.rllib.agents.registry import get_agent_class
+from ray.tune.util import merge_dicts
 
 EXAMPLE_USAGE = """
 Example Usage via RLlib CLI:
@@ -69,22 +70,23 @@ def create_parser(parser_creator=None):
 
 
 def run(args, parser):
-    config = args.config
-    if not config:
-        # Load configuration from file
-        config_dir = os.path.dirname(args.checkpoint)
-        config_path = os.path.join(config_dir, "params.pkl")
-        if not os.path.exists(config_path):
-            config_path = os.path.join(config_dir, "../params.pkl")
-        if not os.path.exists(config_path):
+    config = {}
+    # Load configuration from file
+    config_dir = os.path.dirname(args.checkpoint)
+    config_path = os.path.join(config_dir, "params.pkl")
+    if not os.path.exists(config_path):
+        config_path = os.path.join(config_dir, "../params.pkl")
+    if not os.path.exists(config_path):
+        if not args.config:
             raise ValueError(
                 "Could not find params.pkl in either the checkpoint dir or "
                 "its parent directory.")
+    else:
         with open(config_path, 'rb') as f:
             config = pickle.load(f)
-        if "num_workers" in config:
-            config["num_workers"] = min(2, config["num_workers"])
-
+    if "num_workers" in config:
+        config["num_workers"] = min(2, config["num_workers"])
+    config = merge_dicts(config, args.config)
     if not args.env:
         if not config.get("env"):
             parser.error("the following arguments are required: --env")