Added defaultordereddict.py

defaultordereddict.py

@@ -0,0 +1,46 @@
+"""
+From http://stackoverflow.com/questions/6190331/can-i-do-an-ordered-default-dict-in-python
+"""
+
+from collections import OrderedDict, Callable
+
+class DefaultOrderedDict(OrderedDict):
+    def __init__(self, default_factory=None, *a, **kw):
+        if (default_factory is not None and
+            not isinstance(default_factory, Callable)):
+            raise TypeError('first argument must be callable')
+        OrderedDict.__init__(self, *a, **kw)
+        self.default_factory = default_factory
+
+    def __getitem__(self, key):
+        try:
+            return OrderedDict.__getitem__(self, key)
+        except KeyError:
+            return self.__missing__(key)
+
+    def __missing__(self, key):
+        if self.default_factory is None:
+            raise KeyError(key)
+        self[key] = value = self.default_factory()
+        return value
+
+    def __reduce__(self):
+        if self.default_factory is None:
+            args = tuple()
+        else:
+            args = self.default_factory,
+        return type(self), args, None, None, self.items()
+
+    def copy(self):
+        return self.__copy__()
+
+    def __copy__(self):
+        return type(self)(self.default_factory, self)
+
+    def __deepcopy__(self, memo):
+        import copy
+        return type(self)(self.default_factory,
+                          copy.deepcopy(self.items()))
+    def __repr__(self):
+        return 'OrderedDefaultDict(%s, %s)' % (self.default_factory,
+                                        OrderedDict.__repr__(self))