from UserDict import DictMixin

class OrderedDict(dict, DictMixin):

    def __init__(self, *args, **kwds):

        if len(args) > 1:

            raise TypeError('expected at most 1 arguments, got %d' % len(args))

        try:

            self.__end

        except AttributeError:

            self.clear()

        self.update(*args, **kwds)

    def clear(self):

        self.__end = end = []

        end += [None, end, end]         # sentinel node for doubly linked list

        self.__map = {}                 # key --> [key, prev, next]

        dict.clear(self)

    def __setitem__(self, key, value):

        if key not in self:

            end = self.__end

            curr = end[1]

            curr[2] = end[1] = self.__map[key] = [key, curr, end]

        dict.__setitem__(self, key, value)

    def __delitem__(self, key):

        dict.__delitem__(self, key)

        key, prev, next = self.__map.pop(key)

        prev[2] = next

        next[1] = prev

    def __iter__(self):

        end = self.__end

        curr = end[2]

        while curr is not end:

            yield curr[0]

            curr = curr[2]

    def __reversed__(self):

        end = self.__end

        curr = end[1]

        while curr is not end:

            yield curr[0]

            curr = curr[1]

    def popitem(self, last=True):

        if not self:

            raise KeyError('dictionary is empty')

        if last:

            key = reversed(self).next()

        else:

            key = iter(self).next()

        value = self.pop(key)

        return key, value

    def __reduce__(self):

        items = [[k, self[k]] for k in self]

        tmp = self.__map, self.__end

        del self.__map, self.__end

        inst_dict = vars(self).copy()

        self.__map, self.__end = tmp

        if inst_dict:

            return (self.__class__, (items,), inst_dict)

        return self.__class__, (items,)

    def keys(self):

        return list(self)

    setdefault = DictMixin.setdefault

    update = DictMixin.update

    pop = DictMixin.pop

    values = DictMixin.values

    items = DictMixin.items

    iterkeys = DictMixin.iterkeys

    itervalues = DictMixin.itervalues

    iteritems = DictMixin.iteritems

    def __repr__(self):

        if not self:

            return '%s()' % (self.__class__.__name__,)

        return '%s(%r)' % (self.__class__.__name__, self.items())

    def copy(self):

        return self.__class__(self)

    @classmethod

    def fromkeys(cls, iterable, value=None):

        d = cls()

        for key in iterable:

            d[key] = value

        return d

    def __eq__(self, other):

        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