support fallback in NestedDict.get

Signed-off-by: Zhiyuan Chen <[email protected]>

chanfig/config.py

@@ -428,7 +428,7 @@ def unlocked(self):
             if was_frozen:
                 self.freeze()
 
-    def get(self, name: Any, default: Any = None) -> Any:
+    def get(self, name: Any, default: Any = None, fallback: bool | None = None) -> Any:
         r"""
         Get value from `Config`.
 
@@ -476,7 +476,7 @@ def get(self, name: Any, default: Any = None) -> Any:
         if not self.hasattr("default_factory"):  # did not call super().__init__() in sub-class
             self.setattr("default_factory", Config)
         if name in self or not self.getattr("frozen", False):
-            return super().get(name, default)
+            return super().get(name, default, fallback)
         raise KeyError(name)
 
     @frozen_check

chanfig/flat_dict.py

@@ -716,7 +716,7 @@ def merge(self, *args: Any, overwrite: bool = True, **kwargs: Any) -> FlatDict:
     def _merge(this: FlatDict, that: Iterable, overwrite: bool = True) -> Mapping:
         if not that:
             return this
-        elif isinstance(that, Mapping):
+        if isinstance(that, Mapping):
             that = that.items()
         for key, value in that:
             if key in this and isinstance(this[key], Mapping):

chanfig/nested_dict.py

@@ -149,13 +149,20 @@ class NestedDict(DefaultDict):  # type: ignore # pylint: disable=E1136
 
     convert_mapping: bool = False
     delimiter: str = "."
+    fallback: bool = False
 
     def __init__(
-        self, *args: Any, default_factory: Callable | None = None, convert_mapping: bool = False, **kwargs: Any
+        self,
+        *args: Any,
+        default_factory: Callable | None = None,
+        convert_mapping: bool = False,
+        fallback: bool = False,
+        **kwargs: Any,
     ) -> None:
         super().__init__(default_factory)
         self.merge(*args, **kwargs)
         self.setattr("convert_mapping", convert_mapping)
+        self.setattr("fallback", fallback)
 
     def all_keys(self) -> Generator:
         r"""
@@ -289,7 +296,7 @@ def apply_(self, func: Callable, *args: Any, **kwargs: Any) -> NestedDict:
         apply_(self, func, *args, **kwargs)
         return self
 
-    def get(self, name: Any, default: Any = None) -> Any:
+    def get(self, name: Any, default: Any = None, fallback: bool | None = None) -> Any:
         r"""
         Get value from `NestedDict`.
 
@@ -320,6 +327,7 @@ def get(self, name: Any, default: Any = None) -> Any:
             1013
             >>> d.get('f', 2)
             2
+            >>> d.get('a.b', None)
             >>> d.f
             NestedDict(<class 'chanfig.nested_dict.NestedDict'>, )
             >>> del d.f
@@ -340,12 +348,24 @@ def get(self, name: Any, default: Any = None) -> Any:
         """
 
         delimiter = self.getattr("delimiter", ".")
+        if fallback is None:
+            fallback = self.getattr("fallback", False)
+        fallback_name = name.split(delimiter)[-1] if isinstance(name, str) else name
+        fallback_values = []
         try:
             while isinstance(name, str) and delimiter in name:
+                if fallback and fallback_name in self:
+                    fallback_values.append(self.get(fallback_name))
                 name, rest = name.split(delimiter, 1)
                 self, name = self[name], rest  # pylint: disable=W0642
-        except (AttributeError, TypeError):
+        except (KeyError, AttributeError, TypeError):
+            if fallback and fallback_values:
+                return fallback_values[-1]
+            if default is not Null:
+                return default
             raise KeyError(name) from None
+        if (fallback and fallback_values) and (not isinstance(self, Iterable) or name not in self):
+            return fallback_values[-1]
         # if value is a python dict
         if not isinstance(self, NestedDict):
             if name not in self and default is not Null:
@@ -405,9 +425,9 @@ def set(  # pylint: disable=W0221
         # pylint: disable=W0642
 
         full_name = name
+        delimiter = self.getattr("delimiter", ".")
         if convert_mapping is None:
             convert_mapping = self.getattr("convert_mapping", False)
-        delimiter = self.getattr("delimiter", ".")
         default_factory = self.getattr("default_factory", self.empty)
         try:
             while isinstance(name, str) and delimiter in name:

chanfig/registry.py

@@ -88,8 +88,8 @@ class Registry(NestedDict):  # type: ignore
 
     override: bool = False
 
-    def __init__(self, override: bool = False):
-        super().__init__()
+    def __init__(self, override: bool = False, fallback: bool = False):
+        super().__init__(fallback=fallback)
         self.setattr("override", override)
 
     def register(self, component: Any = None, name: Any | None = None) -> Callable:

tests/test_nested_dict.py

@@ -86,6 +86,11 @@ def test_dropnull(self):
         }
         assert d.dropnull().dict() == {"h": {"j": 1}}
 
+    def test_fallback(self):
+        d = NestedDict({"n.d": 0.5, "n.a.d": 0.1, "n.b.l": 6})
+        assert d.get("n.a.d", fallback=True) == 0.1
+        assert d.get("n.b.d", fallback=True) == 0.5
+
 
 class ConfigDict(NestedDict):
     def __init__(self):