passing additional arguments to json.dump in python2

Question

I'm using json.dump with a custom encoder in python2, and I want to pass an additional parameter to the encoder, this way:

json.dump(data, fp, type, cls=MyEncoder)

Following How to pass parameters to a custom JSONEncoder default() function in Python I wrote the encoder:

class MyEncoder(json.JSONEncoder):
    def __init__(self, type, **kwargs):
        super(MyEncoder, self).__init__(**kwargs)
        self.type = type

    def default(self, obj):
        type = self.type
        if isinstance(obj, datetime):
            # there was the line:

but, in init, the type value is assigned to kwargs['skipkeys'], not to type variable.

What am I missing?

Would it be different in python3?

jwodder · Accepted Answer · 2019-06-08 22:28:45Z

1

According to the documentation, the third argument to json.dumps is the skipkeys argument, and so that's what the type argument in json.dump(data, fp, type, cls=MyEncoder) is treated as; the fact that the variable is named type is irrelevant, as json.dumps never sees that name. In order to make json.dumps see that name, you have to pass type as a keyword argument: json.dump(data, fp, type=type, cls=MyEncoder).

answered Jun 8, 2019 at 22:28

jwodder

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1 Comment

jwodder Over a year ago

@PaoloBenvenuto: Yes, it should.

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