'Override to support the "get_slice" for python3'

def __getitem__(self, index):

    if isinstance(index, slice):
        r = SortedDict(ignore_case=self.ignore_case)
        for k in self.keys()[index]:
            r[k] = self[k]
    else:
        r = super(SortedDict, self).__getitem__(index)
    return r
