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Custom datatypes (like datetime) serialization to/from JSON.

Project description

Serialization of Python types to JSON that “just works”.

Forget errors like:

TypeError: datetime.datetime(...) is not JSON serializable

In addition to (de-)serialization of basic types (provided by simplejson), jsonplus provides support for exact (de-)serialization of other commonly used types, like: tuple/namedtuple, set/frozenset, complex/decimal.Decimal/fractions.Fraction, and datetime/date/time/timedelta.

If the exact representation of types is not your cup of tea, and all you wish for is json.dumps to work on your data structure with non-basic types, accepting the loss of “type-precision” along the way, than you should use the compatibility mode (jsonplus.prefer_compat()).


jsonplus is available as Python package. To install, simply type:

$ pip install jsonplus


You can treat jsonplus as a friendly drop-in replacement for json/simplejson.

>>> import jsonplus as json

>>> x = json.loads('{"a":1,"b":2}')
>>> y = json.dumps(x, indent=4)
>>> z = json.pretty(x)


Let’s start with that beloved datetime.

>>> import jsonplus as json

>>> from datetime import datetime
>>> json.dumps({
...     "x": [4,3],
...     "t":
... })

>>> json.loads(_)
{u'x': [4, 3], u't': datetime.datetime(2013, 9, 6, 23, 38, 55, 819791)}

Similarly for other datetime.* types, like timedelta, date, and time:

>>> from datetime import timedelta, date, time
>>> print(json.pretty({"dt": timedelta(0, 1234567, 123), "d":, "t":}))
    "d": {
        "__class__": "date",
        "__value__": "2013-09-22"
    "dt": {
        "__class__": "timedelta",
        "__value__": {
            "days": 14,
            "microseconds": 123,
            "seconds": 24967
    "t": {
        "__class__": "time",
        "__value__": "23:33:16.335360"

Also, set and complex:

>>> json.dumps([set(range(3)), 1+2j])

>>> json.loads(_)
[set([0, 1, 2]), (1+2j)]

tuple and namedtuple are also preserved:

>>> from collections import namedtuple
>>> Point = namedtuple('Point', ['x', 'y'])

>>> data = json.pretty({"vect": (1, 2, 3), "dot": Point(3, 4)})
>>> print(data)
    "dot": {
        "__class__": "namedtuple",
        "__value__": {
            "fields": [
            "name": "Point",
            "values": [
    "vect": {
        "__class__": "tuple",
        "__value__": [

>>> json.loads(data)
{'vect': (1, 2, 3), 'dot': Point(x=3, y=4)}

Compatibility mode

All types supported in the exact mode are also supported in the compatibility mode. JSON representation differs, however.

In the exact mode, type and value are encoded with JSON Object’s __class__ and __value__ keys, while in the compatibility mode, values are “rounded” to the closest JSON type.

For example, tuple``s and ``set``s are represented with ``JSON Array``s, and ``namedtuple``s are coded as plain ``JSON Object``s. ``Decimal``s are represented as ``JSON Number``s with arbitrary precision (which is lost if decoded as ``float).

To switch between the exact and compatibility modes, use the (thread- local) functions prefer_exact() and prefer_compat():

>>> import jsonplus as json

>>> json.prefer_compat()
# or:
>>> json.prefer(json.COMPAT)

# to go back to (default) exact coding:
>>> json.prefer_exact()

The above tuple/namedtuple example run in compatibility coding mode results with:

>>> json.prefer_compat()
>>> print(json.pretty({"vect": (1, 2, 3), "dot": Point(3, 4)}))
    "point": {
        "x": 3,
        "y": 4
    "vector": [

Dates and times are represented with ISO8601 strings:

>>> json.prefer_compat()
>>> json.dumps({"now":})

So, to be able to decode it as date/time, some additional context has to be provided to the decoder.

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