Serialising an Enum member to JSON

Question:

How do I serialise a Python Enum member to JSON, so that I can deserialise the resulting JSON back into a Python object?

For example, this code:

from enum import Enum    
import json

class Status(Enum):
    success = 0

json.dumps(Status.success)

results in the error:

TypeError: <Status.success: 0> is not JSON serializable

How can I avoid that?

Asked By: Bilal Syed Hussain

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Source

Answers:

The correct answer depends on what you intend to do with the serialized version.

If you are going to unserialize back into Python, see Zero’s answer.

If your serialized version is going to another language then you probably want to use an IntEnum instead, which is automatically serialized as the corresponding integer:

from enum import IntEnum
import json

class Status(IntEnum):
    success = 0
    failure = 1

json.dumps(Status.success)

and this returns:

'0'
Answered By: Ethan Furman

If you want to encode an arbitrary enum.Enum member to JSON and then decode
it as the same enum member (rather than simply the enum member’s value attribute), you can do so by writing a custom JSONEncoder class, and a decoding function to pass as the object_hook argument to json.load() or json.loads():

PUBLIC_ENUMS = {
    'Status': Status,
    # ...
}

class EnumEncoder(json.JSONEncoder):
    def default(self, obj):
        if type(obj) in PUBLIC_ENUMS.values():
            return {"__enum__": str(obj)}
        return json.JSONEncoder.default(self, obj)

def as_enum(d):
    if "__enum__" in d:
        name, member = d["__enum__"].split(".")
        return getattr(PUBLIC_ENUMS[name], member)
    else:
        return d

The as_enum function relies on the JSON having been encoded using EnumEncoder, or something which behaves identically to it.

The restriction to members of PUBLIC_ENUMS is necessary to avoid a maliciously crafted text being used to, for example, trick calling code into saving private information (e.g. a secret key used by the application) to an unrelated database field, from where it could then be exposed (see https://chat.stackoverflow.com/transcript/message/35999686#35999686).

Example usage:

>>> data = {
...     "action": "frobnicate",
...     "status": Status.success
... }
>>> text = json.dumps(data, cls=EnumEncoder)
>>> text
'{"status": {"__enum__": "Status.success"}, "action": "frobnicate"}'
>>> json.loads(text, object_hook=as_enum)
{'status': <Status.success: 0>, 'action': 'frobnicate'}
Answered By: Zero Piraeus

I liked Zero Piraeus’ answer, but modified it slightly for working with the API for Amazon Web Services (AWS) known as Boto.

class EnumEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Enum):
            return obj.name
        return json.JSONEncoder.default(self, obj)

I then added this method to my data model:

    def ToJson(self) -> str:
        return json.dumps(self.__dict__, cls=EnumEncoder, indent=1, sort_keys=True)

I hope this helps someone.

Answered By: Pretzel

I know this is old but I feel this will help people. I just went through this exact problem and discovered if you’re using string enums, declaring your enums as a subclass of str works well for almost all situations:

import json
from enum import Enum

class LogLevel(str, Enum):
    DEBUG = 'DEBUG'
    INFO = 'INFO'

print(LogLevel.DEBUG)
print(json.dumps(LogLevel.DEBUG))
print(json.loads('"DEBUG"'))
print(LogLevel('DEBUG'))

Will output:

LogLevel.DEBUG
"DEBUG"
DEBUG
LogLevel.DEBUG

As you can see, loading the JSON outputs the string DEBUG but it is easily castable back into a LogLevel object. A good option if you don’t want to create a custom JSONEncoder.

Answered By: Justin Carter

If you are using jsonpickle the easiest way should look as below.

from enum import Enum
import jsonpickle


@jsonpickle.handlers.register(Enum, base=True)
class EnumHandler(jsonpickle.handlers.BaseHandler):

    def flatten(self, obj, data):
        return obj.value  # Convert to json friendly format


if __name__ == '__main__':
    class Status(Enum):
        success = 0
        error = 1

    class SimpleClass:
        pass

    simple_class = SimpleClass()
    simple_class.status = Status.success

    json = jsonpickle.encode(simple_class, unpicklable=False)
    print(json)

After Json serialization you will have as expected {"status": 0} instead of 

{"status": {"__objclass__": {"py/type": "__main__.Status"}, "_name_": "success", "_value_": 0}}
Answered By: rafalkasa

In Python >= 3.7, can just use
json.dumps(enum_obj, default=str)

If you want to use the enum value, you can do

json.dumps(enum_obj, default=lambda x: x.value)

or if you want to use the enum name,

json.dumps(enum_obj, default=lambda x: x.name)

Answered By: kai

This worked for me:

class Status(Enum):
    success = 0

    def __json__(self):
        return self.value

Didn’t have to change anything else. Obviously, you’ll only get the value out of this and will need to do some other work if you want to convert the serialized value back into the enum later.

Answered By: DukeSilver

You just need to inherit from str or int class:

from enum import Enum, unique

@unique            
class StatusEnum(int, Enum):
    pending: int = 11                                      
    approved: int = 15                                       
    declined: int = 266

That’s it, it will be serialised using any JSON encoder.

Answered By: Farshid Ashouri

You can even combine the solutions mentioned above with the automatic value creation for Enums. I use this in combination with Pydantic and FastAPI to provide lower case names for a REST API:

from enum import Enum, auto
import json

class StrEnum(str, Enum):
    pass

# this creates nice lowercase and JSON serializable names
# https://docs.python.org/3/library/enum.html#using-automatic-values
class AutoNameLower(StrEnum):
    def _generate_next_value_(name, start, count, last_values):
        return name.lower()

class AutoNameLowerStrEnum(AutoNameLower):
    pass

class MyActualEnum(AutoNameLowerStrEnum):
    THIS = auto()
    THAT = auto()
    FOO = auto()
    BAR = auto()

print(MyActualEnum.THIS)
print(json.dumps(MyActualEnum.THIS))
print(list(MyActualEnum))

Console:

>>> MyActualEnum.THIS
>>> "this"
>>> [<MyActualEnum.THIS: 'this'>, <MyActualEnum.THAT: 'that'>, <MyActualEnum.FOO: 'foo'>, <MyActualEnum.BAR: 'bar'>]
Answered By: Joe