How to use custom Python JSON serializers and deserializers to automatically roundtrip complex types.

gistfile1.py

import json, datetime

class RoundTripEncoder(json.JSONEncoder):
    DATE_FORMAT = "%Y-%m-%d"
    TIME_FORMAT = "%H:%M:%S"
    def default(self, obj):
        if isinstance(obj, datetime.datetime):
            return {
                "_type": "datetime",
                "value": obj.strftime("%s %s" % (
                    self.DATE_FORMAT, self.TIME_FORMAT
                ))
            }
        return super(RoundTripEncoder, self).default(obj)

data = {
    "name": "Silent Bob",
    "dt": datetime.datetime(2013, 11, 11, 10, 40, 32)
}

print json.dumps(data, cls=RoundTripEncoder, indent=2)

import json, datetime
from dateutil import parser

class RoundTripDecoder(json.JSONDecoder):
    def __init__(self, *args, **kwargs):
        json.JSONDecoder.__init__(self, object_hook=self.object_hook, *args, **kwargs)

    def object_hook(self, obj):
        if '_type' not in obj:
            return obj
        type = obj['_type']
        if type == 'datetime':
            return parser.parse(obj['value'])
        return obj

print json.loads(s, cls=RoundTripDecoder)

@Timokasse @simonw I think it is simpler than that, unless I am misunderstanding.

>>> import json
>>> import datetime
>>> data = {
...     "name": "Silent Bob",
...     "dt": datetime.datetime(2013, 11, 11, 10, 40, 32)
... }

# Fails as expected
>>> json.dumps(data)
TypeError: Object of type datetime is not JSON serializable

# Succeeds
>>> json.dumps(data, default=str)
'{"name": "Silent Bob", "dt": "2013-11-11 10:40:32"}'

@andelink Oh great type for the encoder part. However this encoder structure is future proof if you need other types to serialize that might not be serializable as string (but as record) like list of paragraph (that might contains comma).

@Timokasse @foresmac I did a version with the desired condensed shape.
https://gist.github.com/Et7f3/922260074697e585bb492b5f2e7e1166

@setaou does your scanner is equivalent to my trick with except ValueError