fixed amp bug

pytorch_lightning/utils/debugging.py

@@ -12,4 +12,8 @@ class ForkedPdb(pdb.Pdb):
             sys.stdin = open('/dev/stdin')
             pdb.Pdb.interaction(self, *args, **kwargs)
         finally:
-            sys.stdin = _stdin
+            sys.stdin = _stdin
+
+
+class IncompatibleArgumentsException(Exception):
+    pass