Fix getattr on namespaces, closes #2

objtools/collections.py

@@ -3,10 +3,7 @@ This module provides helpers for working with collections (as in abstract
 base classes defined in the ``collections.abc`` standard Python module:
 iterables, iterators, mappings, etc.).
 """
-from typing import (
-    Mapping, MutableMapping, Sequence, Set,
-    Iterable, Iterator, ByteString, Any,
-)
+from typing import Mapping, Dict, Sequence, Set, Iterable, ByteString, Any
 
 
 def namespacify(value: Any) -> Any:
@@ -42,12 +39,11 @@ def namespacify(value: Any) -> Any:
     return value
 
 
-class Namespace(MutableMapping):
+class Namespace(Dict):
     """
-    A class that maps items of a mapping to attributes. Takes the same
-    arguments as a classic ``dict``. Attributes and items are kept in sync;
-    deleting an item deletes the attribute, and updating an item updates the
-    attribute, and vice-versa.
+    A subclass of ``dict`` which allows accessing items using attributes.
+    Attributes and items are kept in sync; deleting an item deletes the
+    attribute, and updating an item updates the attribute, and vice-versa.
 
     Getting an attribute will call :meth:`namespacify` on the returned value,
     to allow easier manipulation of complex structures such as JSON documents:
@@ -60,45 +56,29 @@ class Namespace(MutableMapping):
        42
     """
 
-    def __init__(self, *args: Iterable, **kwargs: Any):
-        """
-        :param \\*args: Mappings or iterables yielding
-           ``(key, value)`` two-tuples.
-        :param \\**kwargs: Key-value pairs set as attributes.
-        """
-        for iterable in (*args, kwargs):
-            if isinstance(iterable, Mapping):
-                iterable = iterable.items()
-            for k, v in iterable:
-                setattr(self, k, v)
-
     def __getitem__(self, name: Any) -> Any:
+        return namespacify(super().__getitem__(name))
+
+    def __getattr__(self, name: str) -> Any:
         try:
-            attr = getattr(self, name)
-        except AttributeError:
-            raise KeyError(repr(name))
-        return namespacify(attr)
+            return self[name]
+        except KeyError:
+            raise AttributeError(repr(name))
 
-    def __setitem__(self, name: Any, value: Any) -> None:
-        setattr(self, name, value)
+    def __setattr__(self, name: str, value: Any) -> None:
+        self[name] = value
 
-    def __delitem__(self, name: Any) -> None:
+    def __delattr__(self, name: str) -> None:
         try:
-            delattr(self, name)
-        except AttributeError:
-            raise KeyError(repr(name))
-
-    def __iter__(self) -> Iterator:
-        return iter(self.__dict__)
-
-    def __len__(self) -> int:
-        return len(self.__dict__)
+            del self[name]
+        except KeyError as e:
+            raise AttributeError(str(e))
 
     def __repr__(self) -> str:
-        return '{}({!r})'.format(self.__class__.__name__, self.__dict__)
+        return '{}({})'.format(self.__class__.__name__, super().__repr__())
 
     def __str__(self) -> str:
-        return str(self.__dict__)
+        return str(dict(self))
 
     def _repr_pretty_(self, p: Any, cycle: bool) -> None:
         # IPython's pretty printing
@@ -106,11 +86,11 @@ class Namespace(MutableMapping):
             p.text('{}(...)'.format(self.__class__.__name__))
         else:
             p.text('{}('.format(self.__class__.__name__))
-            p.pretty(self.__dict__)
+            p.pretty(dict(self))
             p.text(')')
 
     def copy(self) -> 'Namespace':
         """
         Create a shallow copy of this namespace.
         """
-        return self.__class__(self.__dict__)
+        return self.__class__(self)

tests/test_collections.py

@@ -55,7 +55,7 @@ class TestNamespace(TestCase):
     def test_init(self) -> None:
         ns: Namespace = Namespace()
         self.assertDictEqual(dict(ns), {})
-        ns = Namespace({'b': 3}, {'a': 4}, a=1, b=2)
+        ns = Namespace({'b': 3}, a=1, b=2)
         self.assertDictEqual(dict(ns), {'a': 1, 'b': 2})
 
     def test_getitem(self) -> None: