Add functionality to allow addition of new value from yaml (#9)

* Add additional parameter to CfgNode to allow new values

* Format config files for test properly

* Allow addition of new CfgNodes from yaml file

* Format config properly

* Simplify logic for merging configurations

example/config_new_allowed.yaml

@@ -0,0 +1,6 @@
+KWARGS:
+  a: 1  # Test adding of basic value
+  B:
+    c: 2  # Test adding of another node
+    D:
+      e: '3'  # Test adding of nested nodes

example/config_new_allowed_bad.yaml

@@ -0,0 +1,3 @@
+KWARGS:
+  Y:
+    f: 4  # While `KWARGS` allows new nodes, `KWARGS.Y` doesn't, so this should raise an Exception

setup.py

@@ -2,7 +2,7 @@
 
 setup(
     name="yacs",
-    version="0.1.4",
+    version="0.1.5",
     author="Ross Girshick",
     author_email="[email protected]",
     description="Yet Another Configuration System",

yacs/config.py

@@ -28,7 +28,6 @@
 
 import yaml
 
-
 # Flag for py2 and py3 compatibility to use when separate code paths are necessary
 # When _PY2 is False, we assume Python 3 is in use
 _PY2 = False
@@ -70,8 +69,9 @@ class CfgNode(dict):
     IMMUTABLE = "__immutable__"
     DEPRECATED_KEYS = "__deprecated_keys__"
     RENAMED_KEYS = "__renamed_keys__"
+    NEW_ALLOWED = "__new_allowed__"
 
-    def __init__(self, init_dict=None, key_list=None):
+    def __init__(self, init_dict=None, key_list=None, new_allowed=False):
         # Recursively convert nested dictionaries in init_dict into CfgNodes
         init_dict = {} if init_dict is None else init_dict
         key_list = [] if key_list is None else key_list
@@ -108,6 +108,9 @@ def __init__(self, init_dict=None, key_list=None):
             # ),
         }
 
+        # Allow new attributes after initialisation
+        self.__dict__[CfgNode.NEW_ALLOWED] = new_allowed
+
     def __getattr__(self, name):
         if name in self:
             return self[name]
@@ -280,6 +283,9 @@ def raise_key_rename_error(self, full_key):
             )
         )
 
+    def is_new_allowed(self):
+        return self.__dict__[CfgNode.NEW_ALLOWED]
+
 
 def load_cfg(cfg_file_obj_or_str):
     """Load a cfg. Supports loading from:
@@ -382,28 +388,30 @@ def _merge_a_into_b(a, b, root, key_list):
 
     for k, v_ in a.items():
         full_key = ".".join(key_list + [k])
-        # a must specify keys that are in b
-        if k not in b:
+
+        v = copy.deepcopy(v_)
+        v = _decode_cfg_value(v)
+
+        if k in b:
+            v = _check_and_coerce_cfg_value_type(v, b[k], k, full_key)
+            # Recursively merge dicts
+            if isinstance(v, CfgNode):
+                try:
+                    _merge_a_into_b(v, b[k], root, key_list + [k])
+                except BaseException:
+                    raise
+            else:
+                b[k] = v
+        elif b.is_new_allowed():
+            b[k] = v
+        else:
             if root.key_is_deprecated(full_key):
                 continue
             elif root.key_is_renamed(full_key):
                 root.raise_key_rename_error(full_key)
             else:
                 raise KeyError("Non-existent config key: {}".format(full_key))
 
-        v = copy.deepcopy(v_)
-        v = _decode_cfg_value(v)
-        v = _check_and_coerce_cfg_value_type(v, b[k], k, full_key)
-
-        # Recursively merge dicts
-        if isinstance(v, CfgNode):
-            try:
-                _merge_a_into_b(v, b[k], root, key_list + [k])
-            except BaseException:
-                raise
-        else:
-            b[k] = v
-
 
 def _decode_cfg_value(v):
     """Decodes a raw config value (e.g., from a yaml config files or command

yacs/tests.py

@@ -44,6 +44,11 @@ def get_cfg():
         message="Please update your config fil config file.",
     )
 
+    cfg.KWARGS = CN(new_allowed=True)
+    cfg.KWARGS.z = 0
+    cfg.KWARGS.Y = CN()
+    cfg.KWARGS.Y.X = 1
+
     return cfg
 
 
@@ -254,6 +259,10 @@ def test_invalid_type(self):
 
     def test__str__(self):
         expected_str = """
+KWARGS:
+  Y:
+    X: 1
+  z: 0
 MODEL:
   TYPE: a_foo_model
 NUM_GPUS: 8
@@ -273,6 +282,18 @@ def test__str__(self):
         cfg = get_cfg()
         assert str(cfg) == expected_str
 
+    def test_new_allowed(self):
+        cfg = get_cfg()
+        cfg.merge_from_file("example/config_new_allowed.yaml")
+        assert cfg.KWARGS.a == 1
+        assert cfg.KWARGS.B.c == 2
+        assert cfg.KWARGS.B.D.e == '3'
+
+    def test_new_allowed_bad(self):
+        cfg = get_cfg()
+        with self.assertRaises(KeyError):
+            cfg.merge_from_file("example/config_new_allowed_bad.yaml")
+
 
 if __name__ == "__main__":
     logging.basicConfig()