Sergey Sergey - 6 months ago 16
Python Question

How to make a class JSON serializable

How to make a Python class serializable?

A simple class:

class FileItem:
def __init__(self, fname):
self.fname = fname

What should I do to be able to get output of:


Without an error (
FileItem instance at ... is not JSON serializable


Do you have an idea about the expected output? For e.g. will this do?

>>> f  = FileItem("/foo/bar")
>>> magic(f)
'{"fname": "/foo/bar"}'

In that case you can merely call json.dumps(f.__dict__).

If you want more customized output then you will have to subclass JSONEncoder and implement your own custom serialization.

For a trivial example, see below.

>>> from json import JSONEncoder
>>> class MyEncoder(JSONEncoder):
    def default(self, o):
        return o.__dict__    

>>> MyEncoder().encode(f)
'{"fname": "/foo/bar"}'

Then you pass this class into the json.dumps() method as cls kwarg:


If you also want to decode then you'll have to supply a custom object_hook to the JSONDecoder class. For e.g.

>>> def from_json(json_object):
        if 'fname' in json_object:
            return FileItem(json_object['fname'])
>>> f = JSONDecoder(object_hook = from_json).decode('{"fname": "/foo/bar"}')
>>> f
<__main__.FileItem object at 0x9337fac>