不同的node生成的key有重叠的话，在删除时其中一个node后会导致keys和key_node数据不一致

[zxybupt]

在使用这个代码时，发现

len(._consistent_hash.keys) 13920

len(._consistent_hash.key_node) 13919

在get_node时，出现KeyError错误 def get_node(self, string_key): """Given a string key a corresponding node in the hash ring is returned.

    If the hash ring is empty, `None` is returned.
    """
    pos = self.get_node_pos(string_key)
    if pos is None:
        return None
    return self.key_node[self.keys[pos]]

怀疑点 m = hashlib.md5()有冲突的概率

解决方案 def del_nodes(self, nodes): """ Deletes nodes from the ring.

    Nodes is expected to be a list of nodes already
    present in the ring.
    """
    try:
        if not isinstance(nodes, list):
            raise TypeError("The arguments of nodes must be list.")
    except TypeError:
        traceback.print_exc(file=sys.stdout)

    # Delete nodes from the ring.
    for node in nodes:
        if node not in self.nodes:
            continue

        for key in self._node_keys(node):
            self.keys.remove(key)
            del self.key_node[key]

        self.index -= 1
        self.nodes.remove(node)

在 self.keys.remove(key)和del self.key_node[key]时，是不是把self.keys.remove(key)都清理了。