python dict values 不可以序列化

对于python dict 的值 values() 序列化问题，python2 和 python3竟然不一样.

python 2.7 下，dict.values() 可以正常序列化

Python 2.7.15 (default, Jun 17 2018, 12:46:58)
>>> import json
>>> kv = {"key-0": "value-0", "key-1": "value-1"}
>>> json.dumps(kv.values())
'["value-1", "value-0"]'
>>> type(kv.values())
<type 'list'>

python3.7 下，dict.values() 不可以序列化

Python 3.7.1 (default, Nov 28 2018, 11:51:54)
>>> import json
>>> kv = {"key-0": "value-0", "key-1": "value-1"}
>>> type(kv.values())
<class 'dict_values'>
>>> json.dumps(kv)
'{"key-0": "value-0", "key-1": "value-1"}'
>>> json.dumps(kv.values())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python/3.7.1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/usr/local/Cellar/python/3.7.1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/local/Cellar/python/3.7.1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/usr/local/Cellar/python/3.7.1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type dict_values is not JSON serializable

python3 字典值不再是一个列表，而是一个 dict_values 封装数据的类，该类不可以序列化。

解决该问题的方案，就是将 dict_values 转化为可序列化的对象即可，如下.

>>> json.dumps(list(kv.values()))
'["value-0", "value-1"]'