add cfg.set_new_allowed (#44)

yacs/config.py

@@ -325,6 +325,20 @@ def raise_key_rename_error(self, full_key):
     def is_new_allowed(self):
         return self.__dict__[CfgNode.NEW_ALLOWED]
 
+    def set_new_allowed(self, is_new_allowed):
+        """
+        Set this config (and recursively its subconfigs) to allow merging
+        new keys from other configs.
+        """
+        self.__dict__[CfgNode.NEW_ALLOWED] = is_new_allowed
+        # Recursively set new_allowed state
+        for v in self.__dict__.values():
+            if isinstance(v, CfgNode):
+                v.set_new_allowed(is_new_allowed)
+        for v in self.values():
+            if isinstance(v, CfgNode):
+                v.set_new_allowed(is_new_allowed)
+
     @classmethod
     def load_cfg(cls, cfg_file_obj_or_str):
         """

yacs/tests.py

@@ -305,6 +305,10 @@ def test_new_allowed_bad(self):
         with self.assertRaises(KeyError):
             cfg.merge_from_file("example/config_new_allowed_bad.yaml")
 
+        cfg.set_new_allowed(True)
+        cfg.merge_from_file("example/config_new_allowed_bad.yaml")
+        assert cfg.KWARGS.Y.f == 4
+
 
 class TestCfgNodeSubclass(unittest.TestCase):
     def test_merge_cfg_from_file(self):