import sys
try:
    from UserDict import DictMixin
except ImportError:
    from collections import UserDict
    try:
        from collections import MutableMapping as DictMixin
    except ImportError:
        from collections.abc import MutableMapping as 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]
        self.__map = {}
        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 = next(reversed(self))
        else:
            key = next(iter(self))
        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)

    if sys.version_info >= (3, 0):
        setdefault = DictMixin.setdefault
        update = DictMixin.update
        pop = DictMixin.pop
        values = DictMixin.values
        items = DictMixin.items
        iterkeys = DictMixin.keys
        itervalues = DictMixin.values
        iteritems = DictMixin.items
    else:
        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__, list(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 \
                   min(p==q for p, q in  zip(list(self.items()), list(other.items())))
        return dict.__eq__(self, other)

    def __ne__(self, other):
        return not self == other


if __name__ == '__main__':
    d = OrderedDict([('foo',2),('bar',3),('baz',4),('zot',5),('arrgh',6)])
    assert [x for x in d] == ['foo', 'bar', 'baz', 'zot', 'arrgh']