--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/OrderedDict.py	Wed Sep 12 17:10:26 2012 -0400
@@ -0,0 +1,259 @@
+# http://code.activestate.com/recipes/576693/
+# Backport of OrderedDict() class that runs on Python 2.4, 2.5, 2.6, 2.7 and pypy.
+# Passes Python2.7's test suite and incorporates all the latest updates.
+
+try:
+    from thread import get_ident as _get_ident
+except ImportError:
+    from dummy_thread import get_ident as _get_ident
+
+try:
+    from _abcoll import KeysView, ValuesView, ItemsView
+except ImportError:
+    pass
+
+
+class OrderedDict(dict):
+    'Dictionary that remembers insertion order'
+    # An inherited dict maps keys to values.
+    # The inherited dict provides __getitem__, __len__, __contains__, and get.
+    # The remaining methods are order-aware.
+    # Big-O running times for all methods are the same as for regular dictionaries.
+
+    # The internal self.__map dictionary maps keys to links in a doubly linked list.
+    # The circular doubly linked list starts and ends with a sentinel element.
+    # The sentinel element never gets deleted (this simplifies the algorithm).
+    # Each link is stored as a list of length three:  [PREV, NEXT, KEY].
+
+    def __init__(self, *args, **kwds):
+        '''Initialize an ordered dictionary.  Signature is the same as for
+        regular dictionaries, but keyword arguments are not recommended
+        because their insertion order is arbitrary.
+
+        '''
+        if len(args) > 1:
+            raise TypeError('expected at most 1 arguments, got %d' % len(args))
+        try:
+            self.__root
+        except AttributeError:
+            self.__root = root = []                     # sentinel node
+            root[:] = [root, root, None]
+            self.__map = {}
+        self.__update(*args, **kwds)
+
+    def __setitem__(self, key, value, dict_setitem=dict.__setitem__):
+        'od.__setitem__(i, y) <==> od[i]=y'
+        # Setting a new item creates a new link which goes at the end of the linked
+        # list, and the inherited dictionary is updated with the new key/value pair.
+        if key not in self:
+            root = self.__root
+            last = root[0]
+            last[1] = root[0] = self.__map[key] = [last, root, key]
+        dict_setitem(self, key, value)
+
+    def __delitem__(self, key, dict_delitem=dict.__delitem__):
+        'od.__delitem__(y) <==> del od[y]'
+        # Deleting an existing item uses self.__map to find the link which is
+        # then removed by updating the links in the predecessor and successor nodes.
+        dict_delitem(self, key)
+        link_prev, link_next, key = self.__map.pop(key)
+        link_prev[1] = link_next
+        link_next[0] = link_prev
+
+    def __iter__(self):
+        'od.__iter__() <==> iter(od)'
+        root = self.__root
+        curr = root[1]
+        while curr is not root:
+            yield curr[2]
+            curr = curr[1]
+
+    def __reversed__(self):
+        'od.__reversed__() <==> reversed(od)'
+        root = self.__root
+        curr = root[0]
+        while curr is not root:
+            yield curr[2]
+            curr = curr[0]
+
+    def clear(self):
+        'od.clear() -> None.  Remove all items from od.'
+        try:
+            for node in self.__map.itervalues():
+                del node[:]
+            root = self.__root
+            root[:] = [root, root, None]
+            self.__map.clear()
+        except AttributeError:
+            pass
+        dict.clear(self)
+
+    def popitem(self, last=True):
+        '''od.popitem() -> (k, v), return and remove a (key, value) pair.
+        Pairs are returned in LIFO order if last is true or FIFO order if false.
+
+        '''
+        if not self:
+            raise KeyError('dictionary is empty')
+        root = self.__root
+        if last:
+            link = root[0]
+            link_prev = link[0]
+            link_prev[1] = root
+            root[0] = link_prev
+        else:
+            link = root[1]
+            link_next = link[1]
+            root[1] = link_next
+            link_next[0] = root
+        key = link[2]
+        del self.__map[key]
+        value = dict.pop(self, key)
+        return key, value
+
+    # -- the following methods do not depend on the internal structure --
+
+    def keys(self):
+        'od.keys() -> list of keys in od'
+        return list(self)
+
+    def values(self):
+        'od.values() -> list of values in od'
+        return [self[key] for key in self]
+
+    def items(self):
+        'od.items() -> list of (key, value) pairs in od'
+        return [(key, self[key]) for key in self]
+
+    def iterkeys(self):
+        'od.iterkeys() -> an iterator over the keys in od'
+        return iter(self)
+
+    def itervalues(self):
+        'od.itervalues -> an iterator over the values in od'
+        for k in self:
+            yield self[k]
+
+    def iteritems(self):
+        'od.iteritems -> an iterator over the (key, value) items in od'
+        for k in self:
+            yield (k, self[k])
+
+    def update(*args, **kwds):
+        '''od.update(E, **F) -> None.  Update od from dict/iterable E and F.
+
+        If E is a dict instance, does:           for k in E: od[k] = E[k]
+        If E has a .keys() method, does:         for k in E.keys(): od[k] = E[k]
+        Or if E is an iterable of items, does:   for k, v in E: od[k] = v
+        In either case, this is followed by:     for k, v in F.items(): od[k] = v
+
+        '''
+        if len(args) > 2:
+            raise TypeError('update() takes at most 2 positional '
+                            'arguments (%d given)' % (len(args),))
+        elif not args:
+            raise TypeError('update() takes at least 1 argument (0 given)')
+        self = args[0]
+        # Make progressively weaker assumptions about "other"
+        other = ()
+        if len(args) == 2:
+            other = args[1]
+        if isinstance(other, dict):
+            for key in other:
+                self[key] = other[key]
+        elif hasattr(other, 'keys'):
+            for key in other.keys():
+                self[key] = other[key]
+        else:
+            for key, value in other:
+                self[key] = value
+        for key, value in kwds.items():
+            self[key] = value
+
+    __update = update  # let subclasses override update without breaking __init__
+
+    __marker = object()
+
+    def pop(self, key, default=__marker):
+        '''od.pop(k[,d]) -> v, remove specified key and return the corresponding value.
+        If key is not found, d is returned if given, otherwise KeyError is raised.
+
+        '''
+        if key in self:
+            result = self[key]
+            del self[key]
+            return result
+        if default is self.__marker:
+            raise KeyError(key)
+        return default
+
+    def setdefault(self, key, default=None):
+        'od.setdefault(k[,d]) -> od.get(k,d), also set od[k]=d if k not in od'
+        if key in self:
+            return self[key]
+        self[key] = default
+        return default
+
+    def __repr__(self, _repr_running={}):
+        'od.__repr__() <==> repr(od)'
+        call_key = id(self), _get_ident()
+        if call_key in _repr_running:
+            return '...'
+        _repr_running[call_key] = 1
+        try:
+            if not self:
+                return '%s()' % (self.__class__.__name__,)
+            return '%s(%r)' % (self.__class__.__name__, self.items())
+        finally:
+            del _repr_running[call_key]
+
+    def __reduce__(self):
+        'Return state information for pickling'
+        items = [[k, self[k]] for k in self]
+        inst_dict = vars(self).copy()
+        for k in vars(OrderedDict()):
+            inst_dict.pop(k, None)
+        if inst_dict:
+            return (self.__class__, (items,), inst_dict)
+        return self.__class__, (items,)
+
+    def copy(self):
+        'od.copy() -> a shallow copy of od'
+        return self.__class__(self)
+
+    @classmethod
+    def fromkeys(cls, iterable, value=None):
+        '''OD.fromkeys(S[, v]) -> New ordered dictionary with keys from S
+        and values equal to v (which defaults to None).
+
+        '''
+        d = cls()
+        for key in iterable:
+            d[key] = value
+        return d
+
+    def __eq__(self, other):
+        '''od.__eq__(y) <==> od==y.  Comparison to another OD is order-sensitive
+        while comparison to a regular mapping is order-insensitive.
+
+        '''
+        if isinstance(other, OrderedDict):
+            return len(self)==len(other) and self.items() == other.items()
+        return dict.__eq__(self, other)
+
+    def __ne__(self, other):
+        return not self == other
+
+    # -- the following methods are only used in Python 2.7 --
+
+    def viewkeys(self):
+        "od.viewkeys() -> a set-like object providing a view on od's keys"
+        return KeysView(self)
+
+    def viewvalues(self):
+        "od.viewvalues() -> an object providing a view on od's values"
+        return ValuesView(self)
+
+    def viewitems(self):
+        "od.viewitems() -> a set-like object providing a view on od's items"
+        return ItemsView(self)