Python JSON encoder to support datetime?

Question

is there any elegant way to make Python JSON encoder support datetime? some 3rd party module or easy hack?

I am using tornado\'s database wrapper to fetch some rows

Answer 1

I made my own classes for my project:

import datetime
import decimal
import json
import sys

class EnhancedJSONEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime.datetime):
            ARGS = ('year', 'month', 'day', 'hour', 'minute',
                     'second', 'microsecond')
            return {'__type__': 'datetime.datetime',
                    'args': [getattr(obj, a) for a in ARGS]}
        elif isinstance(obj, datetime.date):
            ARGS = ('year', 'month', 'day')
            return {'__type__': 'datetime.date',
                    'args': [getattr(obj, a) for a in ARGS]}
        elif isinstance(obj, datetime.time):
            ARGS = ('hour', 'minute', 'second', 'microsecond')
            return {'__type__': 'datetime.time',
                    'args': [getattr(obj, a) for a in ARGS]}
        elif isinstance(obj, datetime.timedelta):
            ARGS = ('days', 'seconds', 'microseconds')
            return {'__type__': 'datetime.timedelta',
                    'args': [getattr(obj, a) for a in ARGS]}
        elif isinstance(obj, decimal.Decimal):
            return {'__type__': 'decimal.Decimal',
                    'args': [str(obj),]}
        else:
            return super().default(obj)


class EnhancedJSONDecoder(json.JSONDecoder):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, object_hook=self.object_hook,
                         **kwargs)

    def object_hook(self, d): 
        if '__type__' not in d:
            return d
        o = sys.modules[__name__]
        for e in d['__type__'].split('.'):
            o = getattr(o, e)
        args, kwargs = d.get('args', ()), d.get('kwargs', {})
        return o(*args, **kwargs)

if __name__ == '__main__':
    j1 = json.dumps({'now': datetime.datetime.now(),
        'val': decimal.Decimal('9.3456789098765434987654567')},
        cls=EnhancedJSONEncoder)
    print(j1)
    o1 = json.loads(j1, cls=EnhancedJSONDecoder)
    print(o1)

Result:

{"val": {"args": ["9.3456789098765434987654567"], "__type__": "decimal.Decimal"}, "now": {"args": [2014, 4, 29, 11, 44, 57, 971600], "__type__": "datetime.datetime"}}
{'val': Decimal('9.3456789098765434987654567'), 'now': datetime.datetime(2014, 4, 29, 11, 44, 57, 971600)}

References:

• json Documentation
• Mark Hildreth -- Subclassing JSONEncoder and JSONDecoder
• Cédric Krier -- trytond.protocols.jsonrpc source code

Note: It can be made more flexible by passing a custom dictionary with types as keys and args, kwargs as values to the encoder's __init__() and use that (or a default dictionary) in the default() method.