Fix warning (#345)

* fix

* refine warning

Author: ceci3

paddleslim/common/rl_controller/__init__.py

@@ -19,9 +19,7 @@
     import parl
     from .ddpg import *
 except ImportError as e:
-    _logger.warn(
-        "If you want to use DDPG in RLNAS, please pip install parl first. Now states: {}".
-        format(e))
+    pass
 
 from .lstm import *
 from .utils import *

paddleslim/nas/rl_nas.py

@@ -76,6 +76,15 @@ def __init__(self,
         self.save_controller = save_controller
         self.load_controller = load_controller
 
+        if key.upper() in ['DDPG']:
+            try:
+                import parl
+            except ImportError as e:
+                _logger.error(
+                    "If you want to use DDPG in RLNAS, please pip install parl first. Now states: {}".
+                    format(e))
+                os._exit(1)
+
         cls = RLCONTROLLER.get(key.upper())
 
         server_ip, server_port = server_addr