preserve order upon simplification of OrdAttMap

attmap/_att_map_like.py

@@ -176,10 +176,10 @@ def _excl_from_repr(self, k, cls):
         """
         return False
 
-    @staticmethod
-    def _new_empty_basic_map():
+    @abc.abstractmethod
+    def _new_empty_basic_map(self):
         """ Return the empty collection builder for Mapping type simplification. """
-        return dict()
+        pass
 
     def _data_for_repr(self):
         return filter(lambda kv: not self._excl_from_repr(kv[0], self.__class__),

attmap/attmap.py

@@ -53,6 +53,10 @@ def __getattr__(self, item, default=None):
             # Throw up our hands in despair and resort to exception behavior.
             raise AttributeError(item)
 
+    def _new_empty_basic_map(self):
+        """ Return the empty collection builder for Mapping type simplification. """
+        return dict()
+
     @property
     def _transformations(self):
         """

attmap/ordattmap.py

@@ -15,3 +15,6 @@ class OrdAttMap(AttMap, OrderedDict):
     def __init__(self, entries=None):
         super(OrderedDict, self).__init__()
         super(AttMap, self).__init__(entries)
+
+    def _new_empty_basic_map(self):
+        return OrderedDict()