Serializing class instance to JSON

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The basic problem is that the JSON encoder json.dumps() only knows how to serialize a limited set of object types by default, all built-in types. List here: https://docs.python.org/3.3/library/json.html#encoders-and-decoders

One good solution would be to make your class inherit from JSONEncoder and then implement the JSONEncoder.default() function, and make that function emit the correct JSON for your class.

A simple solution would be to call json.dumps() on the .__dict__ member of that instance. That is a standard Python dict and if your class is simple it will be JSON serializable.

class Foo(object):
    def __init__(self):
        self.x = 1
        self.y = 2

foo = Foo()
s = json.dumps(foo) # raises TypeError with "is not JSON serializable"

s = json.dumps(foo.__dict__) # s set to: {"x":1, "y":2}

The above approach is discussed in this blog posting:

    Serializing arbitrary Python objects to JSON using _dict_

And, of course, Python offers a built-in function that accesses .__dict__ for you, called vars().

So the above example can also be done as:

s = json.dumps(vars(foo)) # s set to: {"x":1, "y":2}

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