如何在Python节俭解码由结构索引的映射时避免“TypeError:unhashable type”

文件model.thrift 包含以下节俭模式:

struct Coordinate {
    1: required i32 x;
    2: required i32 y;
}

struct Terrain {
    1: required map<Coordinate, i32> altitude_samples;
}

注意,我们有一个由结构(坐标)索引的地图(海拔高度样本)。

我使用Thrift编译器生成Python编码和解码类:

thrift -gen py model.thrift

我使用以下Python代码从文件中解码地形对象:

#!/usr/bin/env python

import sys
sys.path.append('gen-py')

import thrift.protocol.TBinaryProtocol
import thrift.transport.TTransport
import model.ttypes

def decode_terrain_from_file():
    file = open("terrain.dat", "rb")
    transport = thrift.transport.TTransport.TFileObjectTransport(file)
    protocol = thrift.protocol.TBinaryProtocol.TBinaryProtocol(transport)
    terrain = model.ttypes.Terrain()
    terrain.read(protocol)
    print(terrain)

if __name__ == "__main__":
    decode_terrain_from_file()

运行此程序时,出现以下错误:

(env) $ python py_decode.py 
Traceback (most recent call last):
  File "py_decode.py", line 19, in <module>
    decode_terrain_from_file()
  File "py_decode.py", line 15, in decode_terrain_from_file
    terrain.read(protocol)
  File "gen-py/model/ttypes.py", line 119, in read
    self.altitude_samples[_key5] = _val6
TypeError: unhashable type: 'Coordinate