orjson

orjson is a fast, correct JSON library for Python. It benchmarks as the fastest Python library for JSON and is more correct than the standard json library or third-party libraries. It serializes dataclass and datetime instances by default.

Its serialization performance on fixtures of real data is 2.5x to 9.5x the nearest other library and 4x to 12x the standard library. Its deserialization performance on the same fixtures is 1.2x to 1.3x the nearest other library and 1.4x to 2x the standard library.

Its features and drawbacks compared to other Python JSON libraries:

serializes dataclass instances 30x faster than other libraries
serializes datetime, date, and time instances to RFC 3339 format, e.g., "1970-01-01T00:00:00+00:00"
serializes to bytes rather than str, i.e., is not a drop-in replacement
serializes str without escaping unicode to ASCII, e.g., "好" rather than "\\u597d"
serializes float 10x faster and deserializes twice as fast as other libraries
serializes arbitrary types using a default hook
has strict UTF-8 conformance, more correct than the standard library
has strict JSON conformance in not supporting Nan/Infinity/-Infinity
has an option for strict JSON conformance on 53-bit integers with default support for 64-bit
does not support subclasses by default, requiring use of default hook
does not support pretty printing
does not support sorting dict by keys
does not provide load() or dump() functions for reading from/writing to file-like objects

orjson supports CPython 3.6, 3.7, and 3.8. It distributes wheels for Linux, macOS, and Windows. The manylinux1 wheel differs from PEP 513 in requiring glibc 2.18, released 2013, or later. orjson does not currently support PyPy.

orjson is licensed under both the Apache 2.0 and MIT licenses. The repository and issue tracker is github.com/ijl/orjson, and patches may be submitted there.

Usage
1. Install
2. Serialize
  1. default
  2. option
3. Deserialize
Types
1. dataclass
2. datetime
3. float
4. int
5. str
Testing
Performance
License

Usage

Install

To install a wheel from PyPI:

pip install --upgrade orjson

To build from source requires Rust on the nightly channel. Package a wheel from a PEP 517 source distribution using pip:

pip wheel --no-binary=orjson orjson

There are no runtime dependencies other than libc. orjson is compatible with systems using glibc earlier than 2.18 if compiled on such a system. Tooling does not currently support musl libc.

Serialize

def dumps(
    __obj: Any,
    default: Optional[Callable[[Any], Any]] = ...,
    option: Optional[int] = ...,
) -> bytes: ...

dumps() serializes Python objects to JSON.

It natively serializes str, dict, list, tuple, int, float, bool, dataclasses.dataclass, typing.TypedDict, datetime.datetime, datetime.date, datetime.time, and None instances. It supports arbitrary types through default. It does not serialize subclasses of supported types natively, with the exception of dataclasses.dataclass subclasses.

It raises JSONEncodeError on an unsupported type. This exception message describes the invalid object.

It raises JSONEncodeError on a str that contains invalid UTF-8.

It raises JSONEncodeError on an integer that exceeds 64 bits by default or, with OPT_STRICT_INTEGER, 53 bits.

It raises JSONEncodeError if a dict has a key of a type other than str.

It raises JSONEncodeError if the output of default recurses to handling by default more than 254 levels deep.

It raises JSONEncodeError on circular references.

It raises JSONEncodeError if a tzinfo on a datetime object is incorrect.

JSONEncodeError is a subclass of TypeError. This is for compatibility with the standard library.

default

To serialize a subclass or arbitrary types, specify default as a callable that returns a supported type. default may be a function, lambda, or callable class instance.

>>> import orjson, numpy
>>>
def default(obj):
    if isinstance(obj, numpy.ndarray):
        return obj.tolist()
>>> orjson.dumps(numpy.random.rand(2, 2), default=default)
b'[[0.08423896597867486,0.854121264944197],[0.8452845446981371,0.19227780743524303]]'

If the default callable does not return an object, and an exception was raised within the default function, an exception describing this is raised. If no object is returned by the default callable but also no exception was raised, it falls through to raising JSONEncodeError on an unsupported type.

The default callable may return an object that itself must be handled by default up to 254 times before an exception is raised.

option

To modify how data is serialized, specify option. Each option is an integer constant in orjson. To specify multiple options, mask them together, e.g., option=orjson.OPT_STRICT_INTEGER | orjson.OPT_NAIVE_UTC.

OPT_NAIVE_UTC

Serialize datetime.datetime objects without a tzinfo as UTC. This has no effect on datetime.datetime objects that have tzinfo set.

>>> import orjson, datetime
>>> orjson.dumps(
        datetime.datetime(1970, 1, 1, 0, 0, 0),
    )
b'"1970-01-01T00:00:00"'
>>> orjson.dumps(
        datetime.datetime(1970, 1, 1, 0, 0, 0),
        option=orjson.OPT_NAIVE_UTC,
    )
b'"1970-01-01T00:00:00+00:00"'

OPT_OMIT_MICROSECONDS

Do not serialize the microsecond field on datetime.datetime and datetime.time instances.

>>> import orjson, datetime
>>> orjson.dumps(
        datetime.datetime(1970, 1, 1, 0, 0, 0, 1),
    )
b'"1970-01-01T00:00:00.000001"'
>>> orjson.dumps(
        datetime.datetime(1970, 1, 1, 0, 0, 0, 1),
        option=orjson.OPT_OMIT_MICROSECONDS,
    )
b'"1970-01-01T00:00:00"'

OPT_SERIALIZE_DATACLASS

Serialize dataclasses.dataclass instances. For more, see dataclass.

OPT_STRICT_INTEGER

Enforce 53-bit limit on integers. The limit is otherwise 64 bits, the same as the Python standard library. For more, see int.

OPT_UTC_Z

Serialize a UTC timezone on datetime.datetime instances as Z instead of +00:00.

>>> import orjson, datetime
>>> orjson.dumps(
        datetime.datetime(1970, 1, 1, 0, 0, 0, tzinfo=datetime.timezone.utc),
    )
b'"1970-01-01T00:00:00+00:00"'
>>> orjson.dumps(
        datetime.datetime(1970, 1, 1, 0, 0, 0, tzinfo=datetime.timezone.utc),
        option=orjson.OPT_UTC_Z
    )
b'"1970-01-01T00:00:00Z"'

Deserialize

def loads(__obj: Union[bytes, bytearray, str]) -> Any: ...

loads() deserializes JSON to Python objects. It deserializes to dict, list, int, float, str, bool, and None objects.

bytes, bytearray, and str input are accepted. If the input exists as bytes (was read directly from a source), it is recommended to pass bytes. This has lower memory usage and lower latency.

orjson maintains a cache of map keys for the duration of the process. This causes a net reduction in memory usage by avoiding duplicate strings. The keys must be at most 64 chars to be cached and 512 entries are stored.

It raises JSONDecodeError if given an invalid type or invalid JSON. This includes if the input contains NaN, Infinity, or -Infinity, which the standard library allows, but is not valid JSON.

JSONDecodeError is a subclass of json.JSONDecodeError and ValueError. This is for compatibility with the standard library.

Types

dataclass

orjson serializes instances of dataclasses.dataclass natively. It serializes instances 30x as fast as other libraries and avoids a severe slowdown seen in other libraries compared to serializing dict. To serialize instances, specify option=orjson.OPT_SERIALIZE_DATACLASS. The option is required so that users may continue to use default until the implementation allows customizing instances' serialization.

It is supported to pass all variants of dataclasses, including dataclasses using __slots__ (which yields a modest performance improvement), frozen dataclasses, those with optional or default attributes, and subclasses.

Library	dict (ms)	dataclass (ms)	dataclass vs. dict	vs. orjson
orjson	0.10	0.19	-46%	1
ujson
rapidjson	0.24	6.48	-96%	33
simplejson	1.06	7.94	-86%	40
json	0.92	7.32	-87%	37

This measures orjson serializing instances natively and other libraries using default to serialize the output of dataclasses.asdict(). This can be reproduced using the pydataclass script.

Dataclasses are serialized as maps, with every attribute serialized and in the order given on class definition:

>>> import dataclasses, orjson, typing

@dataclasses.dataclass
class Member:
    id: int
    active: bool = dataclasses.field(default=False)

@dataclasses.dataclass
class Object:
    id: int
    name: str
    members: typing.List[Member]

>>> orjson.dumps(
        Object(1, "a", [Member(1, True), Member(2)]),
        option=orjson.OPT_SERIALIZE_DATACLASS,
    )
b'{"id":1,"name":"a","members":[{"id":1,"active":true},{"id":2,"active":false}]}'

Users may wish to control how dataclass instances are serialized, e.g., to not serialize an attribute or to change the name of an attribute when serialized. orjson may implement support using the metadata mapping on field attributes, e.g., field(metadata={"json_serialize": False}), if use cases are clear.

datetime

orjson serializes datetime.datetime objects to RFC 3339 format, e.g., "1970-01-01T00:00:00+00:00". This is a subset of ISO 8601 and compatible with isoformat() in the standard library.

>>> import orjson, datetime, pendulum
>>> orjson.dumps(
    datetime.datetime(2018, 12, 1, 2, 3, 4, 9, tzinfo=pendulum.timezone('Australia/Adelaide'))
)
b'"2018-12-01T02:03:04.000009+10:30"'
>>> orjson.dumps(
    datetime.datetime.fromtimestamp(4123518902).replace(tzinfo=datetime.timezone.utc)
)
b'"2100-09-01T21:55:02+00:00"'
>>> orjson.dumps(
    datetime.datetime.fromtimestamp(4123518902)
)
b'"2100-09-01T21:55:02"'

datetime.datetime supports instances with a tzinfo that is None, datetime.timezone.utc or a timezone instance from the pendulum, pytz, or dateutil/arrow libraries.

datetime.time objects must not have a tzinfo.

>>> import orjson, datetime
>>> orjson.dumps(datetime.time(12, 0, 15, 290))
b'"12:00:15.000290"'

datetime.date objects will always serialize.

>>> import orjson, datetime
>>> orjson.dumps(datetime.date(1900, 1, 2))
b'"1900-01-02"'

Errors with tzinfo result in JSONEncodeError being raised.

It is faster to have orjson serialize datetime objects than to do so before calling dumps(). If using an unsupported type such as pendulum.datetime, use default.

float

orjson serializes and deserializes floats with no loss of precision and consistent rounding. The same behavior is observed in rapidjson, simplejson, and json. ujson is inaccurate in both serialization and deserialization, i.e., it modifies the data.

orjson.dumps() serializes Nan, Infinity, and -Infinity, which are not compliant JSON, as null:

>>> import orjson, ujson, rapidjson, json
>>> orjson.dumps([float("NaN"), float("Infinity"), float("-Infinity")])
b'[null,null,null]'
>>> ujson.dumps([float("NaN"), float("Infinity"), float("-Infinity")])
OverflowError: Invalid Inf value when encoding double
>>> rapidjson.dumps([float("NaN"), float("Infinity"), float("-Infinity")])
'[NaN,Infinity,-Infinity]'
>>> json.dumps([float("NaN"), float("Infinity"), float("-Infinity")])
'[NaN, Infinity, -Infinity]'

int

JSON only requires that implementations accept integers with 53-bit precision. orjson will, by default, serialize 64-bit integers. This is compatible with the Python standard library and other non-browser implementations. For transmitting JSON to a web browser or other strict implementations, dumps() can be configured to raise a JSONEncodeError on values exceeding the 53-bit range.

>>> import orjson
>>> orjson.dumps(9007199254740992)
b'9007199254740992'
>>> orjson.dumps(9007199254740992, option=orjson.OPT_STRICT_INTEGER)
JSONEncodeError: Integer exceeds 53-bit range
>>> orjson.dumps(-9007199254740992, option=orjson.OPT_STRICT_INTEGER)
JSONEncodeError: Integer exceeds 53-bit range

str

orjson is strict about UTF-8 conformance. This is stricter than the standard library's json module, which will serialize and deserialize UTF-16 surrogates, e.g., "\ud800", that are invalid UTF-8.

If orjson.dumps() is given a str that does not contain valid UTF-8, orjson.JSONEncodeError is raised. If loads() receives invalid UTF-8, orjson.JSONDecodeError is raised.

orjson and rapidjson are the only compared JSON libraries to consistently error on bad input.

>>> import orjson, ujson, rapidjson, json
>>> orjson.dumps('\ud800')
JSONEncodeError: str is not valid UTF-8: surrogates not allowed
>>> ujson.dumps('\ud800')
UnicodeEncodeError: 'utf-8' codec ...
>>> rapidjson.dumps('\ud800')
UnicodeEncodeError: 'utf-8' codec ...
>>> json.dumps('\ud800')
'"\\ud800"'
>>> orjson.loads('"\\ud800"')
JSONDecodeError: unexpected end of hex escape at line 1 column 8: line 1 column 1 (char 0)
>>> ujson.loads('"\\ud800"')
''
>>> rapidjson.loads('"\\ud800"')
ValueError: Parse error at offset 1: The surrogate pair in string is invalid.
>>> json.loads('"\\ud800"')
'\ud800'

Testing

The library has comprehensive tests. There are tests against fixtures in the JSONTestSuite and nativejson-benchmark repositories. It is tested to not crash against the Big List of Naughty Strings. It is tested to not leak memory. It is tested to not crash against and not accept invalid UTF-8. There are integration tests exercising the library's use in web servers (gunicorn using multiprocess/forked workers) and when multithreaded. It also uses some tests from the ultrajson library.

Performance

Serialization and deserialization performance of orjson is better than ultrajson, rapidjson, simplejson, or json. The benchmarks are done on fixtures of real data:

twitter.json, 631.5KiB, results of a search on Twitter for "一", containing CJK strings, dictionaries of strings and arrays of dictionaries, indented.
github.json, 55.8KiB, a GitHub activity feed, containing dictionaries of strings and arrays of dictionaries, not indented.
citm_catalog.json, 1.7MiB, concert data, containing nested dictionaries of strings and arrays of integers, indented.
canada.json, 2.2MiB, coordinates of the Canadian border in GeoJSON format, containing floats and arrays, indented.

Latency

twitter.json serialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	0.75	1297.5	1
ujson	2.06	483.5	2.74
rapidjson	2.12	470.7	2.82
simplejson	3.55	275.2	4.73
json	3.57	277.8	4.75

twitter.json deserialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	3.29	302.3	1
ujson	3.65	281.2	1.11
rapidjson	5.6	179.1	1.7
simplejson	5.19	188.3	1.58
json	5.62	184.2	1.71

github.json serialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	0.08	12363.5	1
ujson	0.2	4834.3	2.55
rapidjson	0.23	4385.4	2.84
simplejson	0.42	2360.3	5.28
json	0.36	2709.1	4.53

github.json deserialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	0.25	3992.4	1
ujson	0.32	3065.1	1.28
rapidjson	0.42	2400.2	1.68
simplejson	0.3	3293.5	1.21
json	0.38	2410	1.54

citm_catalog.json serialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	1.27	746.2	1
ujson	3.63	257.1	2.86
rapidjson	3.52	279.8	2.77
simplejson	14.37	66.6	11.31
json	8.28	120.2	6.52

citm_catalog.json deserialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	5.61	175.8	1
ujson	6.78	146.8	1.21
rapidjson	7.71	129.4	1.37
simplejson	9.01	108.8	1.61
json	8.49	116.1	1.51

canada.json serialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	5.28	189.6	1
ujson
rapidjson	69.38	14.3	13.14
simplejson	99.43	9.4	18.84
json	76.44	12.9	14.48

canada.json deserialization

Library	Median latency (milliseconds)	Operations per second	Relative (latency)
orjson	22.22	45.1	1
ujson
rapidjson	44.56	21.4	2.01
simplejson	42.99	23.2	1.93
json	44.69	21.4	2.01

If a row is blank, the library did not serialize and deserialize the fixture without modifying it, e.g., returning different values for floating point numbers.

Memory

orjson's memory usage when deserializing is similar to or lower than the standard library and other third-party libraries.

This measures, in the first column, RSS after importing a library and reading the fixture, and in the second column, increases in RSS after repeatedly calling loads() on the fixture.

twitter.json

Library	import, read() RSS (MiB)	loads() increase in RSS (MiB)
orjson	12.9	2.8
ujson	12.8	4.6
rapidjson	14.5	6.5
simplejson	13.1	2.7
json	12.5	2.4

github.json

Library	import, read() RSS (MiB)	loads() increase in RSS (MiB)
orjson	12.3	0.3
ujson	12.6	0.5
rapidjson	13.9	0.4
simplejson	12.5	0.3
json	11.7	0.3

citm_catalog.json

Library	import, read() RSS (MiB)	loads() increase in RSS (MiB)
orjson	13.7	8.5
ujson	13.9	12
rapidjson	15.4	30.2
simplejson	14.1	25
json	13.5	24.9

canada.json

Library	import, read() RSS (MiB)	loads() increase in RSS (MiB)
orjson	16.5	17.5
ujson
rapidjson	17.9	19.6
simplejson	16.6	21.3
json	16.0	21.3

Reproducing

The above was measured using Python 3.7.4 on Linux with orjson 2.1.0, ujson 1.35, python-rapidson 0.8.0, and simplejson 3.16.0.

The latency results can be reproduced using the pybench and graph scripts. The memory results can be reproduced using the pymem script.

Name		Name	Last commit message	Last commit date
Latest commit History 215 Commits
bench		bench
ci		ci
data		data
doc		doc
integration		integration
src		src
test		test
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
Cargo.lock		Cargo.lock
Cargo.toml		Cargo.toml
LICENSE-APACHE		LICENSE-APACHE
LICENSE-MIT		LICENSE-MIT
README.md		README.md
build		build
deploy		deploy
graph		graph
orjson.pyi		orjson.pyi
profile		profile
pybench		pybench
pydataclass		pydataclass
pymem		pymem
pyproject.toml		pyproject.toml
pytest		pytest
rust-toolchain		rust-toolchain
setup.py		setup.py

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orjson

Usage

Install

Serialize

default

option

OPT_NAIVE_UTC

OPT_OMIT_MICROSECONDS

OPT_SERIALIZE_DATACLASS

OPT_STRICT_INTEGER

OPT_UTC_Z

Deserialize

Types

dataclass

datetime

float

int

str

Testing

Performance

Latency

twitter.json serialization

twitter.json deserialization

github.json serialization

github.json deserialization

citm_catalog.json serialization

citm_catalog.json deserialization

canada.json serialization

canada.json deserialization

Memory

twitter.json

github.json

citm_catalog.json

canada.json

Reproducing

License

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