Merge pull request #3815 from atombrella/keys_dict_3786

Fixes #3786

Author: jpadilla

rest_framework/settings.py

@@ -196,7 +196,7 @@ def user_settings(self):
         return self._user_settings
 
     def __getattr__(self, attr):
-        if attr not in self.defaults.keys():
+        if attr not in self.defaults:
             raise AttributeError("Invalid API setting: '%s'" % attr)
 
         try: