Dictionary/List subclass their native types

yorm/container.py

@@ -17,32 +17,32 @@ def __init__(cls, name, bases, nmspc):
         cls.yorm_attrs = {}
 
 
-class _dict(dict):
+class AttributeDict(dict):
 
     """A `dict` with keys available as attributes."""
 
     def __init__(self, *args, **kwargs):
-        super(dict2, self).__init__(*args, **kwargs)
+        super(AttributeDict, self).__init__(*args, **kwargs)
         self.__dict__ = self
 
 
-class Dictionary(dict, metaclass=ContainerMeta):
+class Dictionary(AttributeDict, metaclass=ContainerMeta):
 
     """Base class for a dictionary of attribute converters."""
 
-    TYPE = _dict
-
     @classmethod
     def to_value(cls, obj):  # pylint: disable=E0213
         """Convert all loaded values back to its original attribute types."""
         if cls is Dictionary:
             msg = "Dictionary class must be subclassed to use"
             raise NotImplementedError(msg)
 
-        value = cls.TYPE()
-        yorm_attrs = cls.yorm_attrs.copy()
+        # Create an uninitialized object with keys as attributes
+        value = cls.__new__(cls)
+        value.__dict__ = value
 
         # Convert object attributes to a dictionary
+        yorm_attrs = cls.yorm_attrs.copy()
         if isinstance(obj, cls):
             items = obj.__dict__.items()
             dictionary = {k: v for k, v in items if k in yorm_attrs}
@@ -107,7 +107,7 @@ def to_dict(obj):
             return {}
 
 
-class List(metaclass=ContainerMeta):
+class List(list, metaclass=ContainerMeta):
 
     """Base class for a homogeneous list of attribute converters."""
 
@@ -126,7 +126,7 @@ def to_value(cls, obj):  # pylint: disable=E0213
         if not cls.item_type:
             raise NotImplementedError("List subclass must specify item type")
 
-        value = []
+        value = cls.__new__(cls)
 
         for item in cls.to_list(obj):
             value.append(cls.item_type.to_value(item))

yorm/test/test_container.py

@@ -25,6 +25,7 @@ class SampleDictionaryWithInitialization(Dictionary):
     """Sample dictionary container with initialization."""
 
     def __init__(self, var1, var2, var3):
+        super().__init__()
         self.var1 = var1
         self.var2 = var2
         self.var3 = var3
@@ -88,9 +89,13 @@ def test_not_implemented(self):
 
     def test_dict_as_object(self):
         """Verify a `Dictionary` can be used as an attribute."""
-        dictionary = SampleDictionaryWithInitialization(1, 2, 3)
+        dictionary = SampleDictionaryWithInitialization(1, 2, 3.0)
         value = {'var1': 1, 'var2': '2'}
-        assert value == dictionary.to_value(dictionary)
+        value2 = dictionary.to_value(dictionary)
+        assert value == value2
+        assert 1 == value2.var1
+        assert '2' == value2.var2
+        assert not hasattr(value2, 'var3')  # lost in conversion
 
 
 class TestList: