Why does json serialization of datetime objects in python not work out of the box for datetime objects

Question

Why does the json serialization not work for datetime objects . As I understand json serialization the basic idea for any object can be call the __str__ builtin function and then urlencode the object that you get as a response. But in case of datetime i get the following error

TypeError: datetime.datetime(2012, 5, 23, 18, 38, 23, 37566) is not JSON serializable

while there is a __str__ i.e a way of stringifying the object already available , But it seems like a conscious decision to not do it , why would that be the case?

Answer 1

No it doesn't work that way in json module. The module provides you with a default encoder: json.JSONEncoder. You need to extend this to provide your implementation of default method to serialize objects. Something like this:

import json
import datetime
from time import mktime

class MyEncoder(json.JSONEncoder):

    def default(self, obj):
        if isinstance(obj, datetime.datetime):
            return int(mktime(obj.timetuple()))

        return json.JSONEncoder.default(self, obj)

print json.dumps(obj, cls=MyEncoder)

As others correctly pointed out, the reason is that the standard for json does not specify how date time can be represented.