An ultra-fast Python 3 implementation of a JSON encoder for Python objects designed to be compatible with native JSON decoders in various web browsers.

Can either encode to a python string (see dumps ) or a sequence of bytes (see dumpb ). The string returned by dumps() is guaranteed to have only 7-bit ASCII characters [1] and dumps(obj).encode('ascii') = dumpb(obj) .

Supports a special encoder class method encode_hook(obj) which, if present, is applied to the input object and the rest of the processing is applied to the output of encode_hook(). Note: encode_hook() should always return an object; for objects which should not be specially encoded encode_hook() should return the original object.

Supports custom encoders by using objects’ __mm_json__() or __mm_serialize__() method, if available. It is guaranteed that for all non-native types __mm_json__ and then __mm_serialize__ will be tried before any other attempt to encode the object [2]. The output of __mm_serialize__ is in turn encoded as any other object (and may in turn have an __mm_serialize__ method or not be supported).

Natively supports strings, integers, floats, True, False, None, lists, tuples, dicts, sets, frozensets, collections.OrderedDicts, colections.Set, collections.Sequence [3], collections.Mapping, uuid.UUIDs [4], decimal.Decimals, datetime.datetime and objects derived form all listed objects.

For all objects which could not be encoded in any other way an attempt is made to convert an object to an encodeable one using Encoder.default(obj) method. If Encoder.default succeeds, the output is again encoded as any other object.

In case there is a need to custom-handle natively supported primitive types, an Encoder.encode_hook method exists.

Examples Encoding custom objects: >>> from metamagic.json import dumps, dumpb >>> class Foo: ... def __mm_serialize__(self): ... return "Im foo" ... >>> dumps(Foo()) '"Im foo"' >>> dumps({Foo(): 123}) '{"Im foo":123}' Dumping straight to bytes: >>> dumpb(Foo()) b'"Im foo"' Bypassing serialization for JSON buffers: >>> class JSONData: ... def __init__(self, data): ... self.data = data ... ... def __mm_json__(self): ... return self.data >>> a = JSONData('["abc", "def"]') >>> dumps([1,2,3,a]) '[1,2,3,["abc", "def"]]'

Exceptions raised Both dumps() and dumpb() raise a TypeError for unsupported objects and for all dictionary keys which are not strings (or UUIDs [5]) and which are not representable as strings (or UUIDs) by their __mm_serialize__ method.

and raise a TypeError for unsupported objects and for all dictionary keys which are not strings (or UUIDs [5]) and which are not representable as strings (or UUIDs) by their method. default() raises a TypeError for all unsupported objects, and overwritten default() is also expected to raise a TypeError for all objects it does not support.

raises a TypeError for all unsupported objects, and overwritten is also expected to raise a TypeError for all objects it does not support. When encoding integers, dumps() and dumpb() raise a ValueError if integer value is greater than the maximum integer value supported by JavaScript ( 9007199254740992 , see http://ecma262-5.com/ELS5_HTML.htm#Section_8.5).

and raise a ValueError if integer value is greater than the maximum integer value supported by JavaScript ( , see http://ecma262-5.com/ELS5_HTML.htm#Section_8.5). When encoding a nested object a ValueError is raised when going deeper than the allowed nesting level (100 by default, can be overwritten by passing the desired value as the second argument to dumps() and dumpb() methods)

Benchmarks Array with 256 short ascii strings: std json: 2.6581 sec, 11286 req/sec mm c json: 0.90321 sec, 33214 req/sec ( 2.9x ) mm c 1ini: 0.85578 sec, 35055 req/sec ( 3.1x ) mm c dumpb: 0.84517 sec, 35495 req/sec ( 3.1x ) marshal: 1.77567 sec, 16895 req/sec Array with 2048 3-char ascii strings: std json: 0.47259 sec, 4231 req/sec mm c json: 0.12481 sec, 16024 req/sec ( 3.8x ) mm c 1ini: 0.12261 sec, 16311 req/sec ( 3.9x ) mm c dumpb: 0.11732 sec, 17047 req/sec ( 4.0x ) marshal: 0.41334 sec, 4838 req/sec Array with 256 long ascii strings: std json: 1.30821 sec, 3822 req/sec mm c json: 0.47144 sec, 10605 req/sec ( 2.8x ) mm c 1ini: 0.44159 sec, 11322 req/sec ( 3.0x ) mm c dumpb: 0.4346 sec, 11504 req/sec ( 3.0x ) marshal: 0.85593 sec, 5841 req/sec Array with 256 long utf-8 strings: std json: 1.52419 sec, 1312 req/sec mm c json: 1.4438 sec, 1385 req/sec ( 1.1x ) mm c 1ini: 1.43666 sec, 1392 req/sec ( 1.1x ) mm c dumpb: 1.40142 sec, 1427 req/sec ( 1.1x ) marshal: 1.3413 sec, 1491 req/sec Medium complex object: std json: 3.5078 sec, 2850 req/sec mm c json: 1.45764 sec, 6860 req/sec ( 2.4x ) mm c 1ini: 1.43357 sec, 6975 req/sec ( 2.4x ) mm c dumpb: 1.47626 sec, 6773 req/sec ( 2.4x ) marshal: 1.04175 sec, 9599 req/sec Array with 256 doubles: std json: 3.37919 sec, 2959 req/sec mm c json: 2.23615 sec, 4471 req/sec ( 1.5x ) mm c 1ini: 2.48201 sec, 4028 req/sec ( 1.4x ) mm c dumpb: 2.23184 sec, 4480 req/sec ( 1.5x ) marshal: 0.14098 sec, 70932 req/sec Array with 256 ints: std json: 1.0185 sec, 19636 req/sec mm c json: 0.2752 sec, 72674 req/sec ( 3.7x ) mm c 1ini: 0.25349 sec, 78898 req/sec ( 4.0x ) mm c dumpb: 0.28252 sec, 70791 req/sec ( 3.6x ) marshal: 0.15442 sec, 129516 req/sec Array with 256 small ints: std json: 1.04397 sec, 191576 req/sec mm c json: 0.28152 sec, 710429 req/sec ( 3.7x ) mm c 1ini: 0.09222 sec, 2168726 req/sec ( 11.3x ) mm c dumpb: 0.27627 sec, 723929 req/sec ( 3.8x ) marshal: 0.08306 sec, 2407897 req/sec Array with 256 Decimals: std json: failed to serialize mm c json: 0.77161 sec, 10367 req/sec ( 0.0x ) mm c 1ini: 0.76022 sec, 10523 req/sec ( 0.0x ) mm c dumpb: 0.78671 sec, 10168 req/sec ( 0.0x ) marshal: failed to serialize Array with 256 True values: std json: 2.08432 sec, 38381 req/sec mm c json: 0.47159 sec, 169638 req/sec ( 4.4x ) mm c 1ini: 0.39814 sec, 200934 req/sec ( 5.2x ) mm c dumpb: 0.45191 sec, 177026 req/sec ( 4.6x ) marshal: 0.24776 sec, 322893 req/sec Array with 256 False values: std json: 2.0099 sec, 39802 req/sec mm c json: 0.50992 sec, 156887 req/sec ( 3.9x ) mm c 1ini: 0.43001 sec, 186042 req/sec ( 4.7x ) mm c dumpb: 0.50839 sec, 157359 req/sec ( 4.0x ) marshal: 0.25551 sec, 313099 req/sec Array with 256 dict{string, int} pairs: std json: 1.96227 sec, 4076 req/sec mm c json: 0.36569 sec, 21876 req/sec ( 5.4x ) mm c 1ini: 0.34565 sec, 23144 req/sec ( 5.7x ) mm c dumpb: 0.36583 sec, 21868 req/sec ( 5.4x ) marshal: 0.51862 sec, 15425 req/sec Array with 256 dict-based{string, int} pairs: std json: 4.20194 sec, 1903 req/sec mm c json: 3.74071 sec, 2138 req/sec ( 1.1x ) mm c 1ini: 3.70554 sec, 2158 req/sec ( 1.1x ) mm c dumpb: 3.77039 sec, 2121 req/sec ( 1.1x ) marshal: failed to serialize Array with 256 orderedDict{string, int} pairs: std json: 2.31765 sec, 431 req/sec mm c json: 0.70724 sec, 1413 req/sec ( 3.3x ) mm c 1ini: 0.69506 sec, 1438 req/sec ( 3.3x ) mm c dumpb: 0.70373 sec, 1420 req/sec ( 3.3x ) marshal: failed to serialize Dict with 256 arrays with 256 dict{string, int} pairs: std json: 3.78828 sec, 13 req/sec mm c json: 0.69496 sec, 71 req/sec ( 5.5x ) mm c 1ini: 0.69522 sec, 71 req/sec ( 5.4x ) mm c dumpb: 0.68382 sec, 73 req/sec ( 5.5x ) marshal: 1.02776 sec, 48 req/sec