Python Enum Encoding for JSON

Question

I have a dictionary where some of the keys are instances of Enum (subclasses of enum.Enum). I am trying to encode a dictionary into a JSON string using the custom JSON Encoder class in accordance with the documentation . All I want is to make the keys in the outputted JSON be Enum name strings. For example, { TestEnum.one : somevalue }will be encoded to { "one" : somevalue }.

I wrote a simple test case, shown below, which I tested in pure virtualenv:

import json

from enum import Enum

class TestEnum(Enum):
    one = "first"
    two = "second"
    three = "third"

class TestEncoder(json.JSONEncoder):
    """ Custom encoder class """

    def default(self, obj):

        print("Default method called!")

        if isinstance(obj, TestEnum):
            print("Seen TestEnum!")
            return obj.name

        return json.JSONEncoder.default(self, obj)

def encode_enum(obj):
    """ Custom encoder method """

    if isinstance(obj, TestEnum):
        return obj.name
    else:
        raise TypeError("Don't know how to decode this")

if __name__ == "__main__":

    test = {TestEnum.one : "This",
            TestEnum.two : "should",
            TestEnum.three : "work!"}

    # Test dumps with Encoder method
    #print("Test with encoder method:")
    #result = json.dumps(test, default=encode_enum)
    #print(result)

    # Test dumps with Encoder Class
    print("Test with encoder class:")
    result = json.dumps(test, cls=TestEncoder)
    print(result)

( Python 3.6.1). TypeError: keys must be a string, ( cls json.dumps), , ? default json.dumps, .

, IntEnum, , Enum . , , Enum, . enum.Enum isinstance?

, TypeError, json.dumps. :

$ python3 enum_test.py

Test with encoder class
Traceback (most recent call last):
  File "enum_test.py", line 59, in <module>
    result = json.dumps(test, cls=TestEncoder)
  File "/usr/lib64/python3.6/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "/usr/lib64/python3.6/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/lib64/python3.6/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
TypeError: keys must be a string

, , encode JSONEncoder , , Enum ( if iterencode), Enum?

!

Answer 1

, JSON, , . ; default , .

:

def convert_keys(obj, convert=str):
    if isinstance(obj, list):
        return [convert_keys(i, convert) for i in obj]
    if not isinstance(obj, dict):
        return obj
    return {convert(k): convert_keys(v, convert) for k, v in obj.items()}

json.dumps(convert_keys(test))

. , ; :

def enum_names(key):
    if isinstance(key, TestEnum):
        return key.name
    return str(key)

json.dumps(convert_keys(test, enum_names))

JSON:

def names_to_enum(key):
    try:
        return TestEnum[key]
    except KeyError:
        return key

convert_keys(json.loads(json_data), names_to_enum)

:

>>> def enum_names(key):
...     if isinstance(key, TestEnum):
...         return key.name
...     return str(key)
...
>>> json_data = json.dumps(convert_keys(test, enum_names))
>>> json_data
'{"one": "This", "two": "should", "three": "work!"}'
>>> def names_to_enum(key):
...     try:
...         return TestEnum[key]
...     except KeyError:
...         return key
...
>>> convert_keys(json.loads(json_data), names_to_enum)
{<TestEnum.one: 'first'>: 'This', <TestEnum.two: 'second'>: 'should', <TestEnum.three: 'third'>: 'work!'}