def load(self):
        if os.path.exists(self.path):
            with open(self.path, 'r') as f:
                self.body_labels = collections.OrderedDict(json.load(f))
def _getN(self, n):
        n -= 1
        p = self.head
        while n:
            p = p.next
            n -= 1
        return p