python json对象序列化奇怪的结果

Question

I am experiencing a strange serialization "effect" that I cannot figure out why it is happening.

Essentially, one property is being represented as expected and another is not. For example, based on the test below I am expecting to get: {"source_system": "ABC", "target_system": "DEF"} not {"source_system": ["ABC"], "target_system": "DEF"}

Seems to think the one property source_system is a tuple but I cannot figure out why... likely I am being blind.

I get the same result with json library as with jsonpickle as shown in the example

import json
import jsonpickle

class testclass(object):
    def __init__(self,
                 _source_system = "",
                 _target_system = ""
                 ):

        self.source_system = _source_system,
        self.target_system = _target_system

    def to_JSON(self):
        return json.dumps(self, default=lambda o: o.__dict__, sort_keys=True, indent=4)    
        # return jsonpickle.encode(self, unpicklable=False)   


def main():
    test = testclass(_source_system = 'ABC', _target_system='DEF')

    print(test.to_JSON())                 
    print(jsonpickle.encode(test, unpicklable=False))
    print(jsonpickle.encode(test))

#============================================================================
if __name__ == '__main__':
    main()

and the results are:

{
    "source_system": [
        "ABC"
    ], 
    "target_system": "DEF"
}
{"source_system": ["ABC"], "target_system": "DEF"}
{"py/object": "__main__.testclass", "source_system": {"py/tuple": ["ABC"]}, "target_system": "DEF"}

Why does it think source_system is a tuple and putting it in [] list brackets ? And, why are both properties not be treated/serialized the same ?

Answer 1

The line

self.source_system = _source_system,

has a trailing comma, so self.source_system is a tuple.

Answer 2

As stated by @fimnor removing the comma inside your __init__ function should do the trick. (May be he will make his comment in an answer, mine here just to explain.)

class testclass(object):
    def __init__(self,
             _source_system = "",
             _target_system = ""
             ):

    self.source_system = _source_system,
    self.target_system = _target_system

def to_JSON(self):
    return json.dumps(self, default=lambda o: o.__dict__, sort_keys=True, indent=4)    
    # return jsonpickle.encode(self, unpicklable=False)

The comma after _source_system in your __init__ makes it a one-tuple and therefore it is converted to JavaScript array. self.source_system = _source_system, is the same as self.source_system = (_source_system,) .