:mod:`simplejson` --- JSON encoder and decoder
.. module:: simplejson
:synopsis: Encode and decode the JSON format... moduleauthor:: Bob Ippolito <bob@redivi.com>.. sectionauthor:: Bob Ippolito <bob@redivi.com>
JSON (JavaScript Object Notation), specified by RFC 7159 (which obsoletes RFC 4627) and by ECMA-404, is a lightweight data interchange format inspired by JavaScript object literal syntax (although it is not a strict subset of JavaScript [1] ).
:mod:`simplejson` is a simple, fast, complete, correct and extensible JSON encoder and decoder for Python. It is pure Python code with no dependencies, but includes an optional C extension for a serious speed boost.
:mod:`simplejson` exposes an API familiar to users of the standard library :mod:`marshal` and :mod:`pickle` modules. It is the externally maintained version of the :mod:`json` library, but maintains compatibility with the latest Python 3.8+ releases back to Python 3.3 as well as the legacy Python 2.5 - Python 2.7 releases.
Development of simplejson happens on Github: http://github.com/simplejson/simplejson
Encoding basic Python object hierarchies:
>>> import simplejson as json
>>> json.dumps(['foo', {'bar': ('baz', None, 1.0, 2)}])
'["foo", {"bar": ["baz", null, 1.0, 2]}]'
>>> print(json.dumps("\"foo\bar"))
"\"foo\bar"
>>> print(json.dumps(u'\u1234'))
"\u1234"
>>> print(json.dumps('\\'))
"\\"
>>> print(json.dumps({"c": 0, "b": 0, "a": 0}, sort_keys=True))
{"a": 0, "b": 0, "c": 0}
>>> from simplejson.compat import StringIO
>>> io = StringIO()
>>> json.dump(['streaming API'], io)
>>> io.getvalue()
'["streaming API"]'Compact encoding:
>>> import simplejson as json
>>> obj = [1,2,3,{'4': 5, '6': 7}]
>>> json.dumps(obj, separators=(',', ':'), sort_keys=True)
'[1,2,3,{"4":5,"6":7}]'Pretty printing:
>>> import simplejson as json
>>> print(json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4 * ' '))
{
"4": 5,
"6": 7
}Decoding JSON:
>>> import simplejson as json
>>> obj = ['foo', {'bar': ['baz', None, 1.0, 2]}]
>>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]') == obj
True
>>> json.loads('"\\"foo\\bar"') == '"foo\x08ar'
True
>>> from simplejson.compat import StringIO
>>> io = StringIO('["streaming API"]')
>>> json.load(io)[0] == 'streaming API'
TrueUsing Decimal instead of float:
>>> import simplejson as json
>>> from decimal import Decimal
>>> json.loads('1.1', use_decimal=True) == Decimal('1.1')
True
>>> json.dumps(Decimal('1.1'), use_decimal=True) == '1.1'
TrueSpecializing JSON object decoding:
>>> import simplejson as json
>>> def as_complex(dct):
... if '__complex__' in dct:
... return complex(dct['real'], dct['imag'])
... return dct
...
>>> json.loads('{"__complex__": true, "real": 1, "imag": 2}',
... object_hook=as_complex)
(1+2j)
>>> import decimal
>>> json.loads('1.1', parse_float=decimal.Decimal) == decimal.Decimal('1.1')
TrueSpecializing JSON object encoding:
>>> import simplejson as json
>>> def encode_complex(obj):
... if isinstance(obj, complex):
... return [obj.real, obj.imag]
... raise TypeError(repr(obj) + " is not JSON serializable")
...
>>> json.dumps(2 + 1j, default=encode_complex)
'[2.0, 1.0]'
>>> json.JSONEncoder(default=encode_complex).encode(2 + 1j)
'[2.0, 1.0]'
>>> ''.join(json.JSONEncoder(default=encode_complex).iterencode(2 + 1j))
'[2.0, 1.0]'Using :mod:`simplejson.tool` from the shell to validate and pretty-print:
$ echo '{"json":"obj"}' | python -m simplejson.tool
{
"json": "obj"
}
$ echo '{ 1.2:3.4}' | python -m simplejson.tool
Expecting property name enclosed in double quotes: line 1 column 3 (char 2)Parsing multiple documents serialized as JSON lines (newline-delimited JSON):
>>> import simplejson as json
>>> def loads_lines(docs):
... for doc in docs.splitlines():
... yield json.loads(doc)
...
>>> sum(doc["count"] for doc in loads_lines('{"count":1}\n{"count":2}\n{"count":3}\n'))
6Serializing multiple objects to JSON lines (newline-delimited JSON):
>>> import simplejson as json
>>> def dumps_lines(objs):
... for obj in objs:
... yield json.dumps(obj, separators=(',',':')) + '\n'
...
>>> ''.join(dumps_lines([{'count': 1}, {'count': 2}, {'count': 3}]))
'{"count":1}\n{"count":2}\n{"count":3}\n'Note
JSON is a subset of YAML 1.2. The JSON produced by this module's default settings (in particular, the default separators value) is also a subset of YAML 1.0 and 1.1. This module can thus also be used as a YAML serializer.
.. function:: dump(obj, fp, skipkeys=False, ensure_ascii=True, \
check_circular=True, allow_nan=True, cls=None, \
indent=None, separators=None, encoding='utf-8', \
default=None, use_decimal=True, \
namedtuple_as_object=True, tuple_as_array=True, \
bigint_as_string=False, sort_keys=False, \
item_sort_key=None, for_json=None, ignore_nan=False, \
int_as_string_bitcount=None, iterable_as_array=False, **kw)
Serialize *obj* as a JSON formatted stream to *fp*
(a ``.write()``-supporting file-like object) using this
:ref:`conversion table <py-to-json-table>`.
The :mod:`simplejson` module will produce :class:`str` objects in
Python 3, not :class:`bytes` objects. Therefore, ``fp.write()`` must
support :class:`str` input.
See :func:`dumps` for a description of each argument. The only difference
is that this function writes the resulting JSON document to *fp* instead
of returning it.
.. note::
When using Python 2, if *ensure_ascii* is set to false,
some chunks written to *fp* may be :class:`unicode` instances, subject
to normal Python :class:`str` to :class:`unicode` coercion rules.
Unless ``fp.write()`` explicitly understands :class:`unicode`
(as in :func:`codecs.getwriter`) this is likely to cause an error.
It's best to leave the default settings, because they are safe and it
is highly optimized.
.. function:: dumps(obj, skipkeys=False, ensure_ascii=True, \
check_circular=True, allow_nan=True, cls=None, \
indent=None, separators=None, encoding='utf-8', \
default=None, use_decimal=True, \
namedtuple_as_object=True, tuple_as_array=True, \
bigint_as_string=False, sort_keys=False, \
item_sort_key=None, for_json=None, ignore_nan=False, \
int_as_string_bitcount=None, iterable_as_array=False, **kw)
Serialize *obj* to a JSON formatted :class:`str`.
If *skipkeys* is true (default: ``False``), then dict keys that are not
of a basic type (:class:`str`, :class:`int`, :class:`long`,
:class:`float`, :class:`bool`, ``None``) will be skipped instead of
raising a :exc:`TypeError`.
.. note::
When using Python 2, both :class:`str` and :class:`unicode` are
considered to be basic types that represent text.
If *ensure_ascii* is false (default: ``True``), then the output may
contain non-ASCII characters, so long as they do not need to be escaped
by JSON. When it is true, all non-ASCII characters are escaped.
.. note::
When using Python 2, if *ensure_ascii* is set to false,
the result may be a :class:`unicode` object. By default, as a memory
optimization, the result would be a :class:`str` object.
If *check_circular* is false (default: ``True``), then the circular
reference check for container types will be skipped and a circular
reference will result in an :exc:`OverflowError` (or worse).
If *allow_nan* is false (default: ``True``), then it will be a
:exc:`ValueError` to serialize out of range :class:`float` values
(``nan``, ``inf``, ``-inf``) in strict compliance of the original
JSON specification. If *allow_nan* is true, their JavaScript equivalents
will be used (``NaN``, ``Infinity``, ``-Infinity``). See also *ignore_nan*
for ECMA-262 compliant behavior.
If *indent* is a string, then JSON array elements and object members
will be pretty-printed with a newline followed by that string repeated
for each level of nesting. ``None`` (the default) selects the most compact
representation without any newlines. For backwards compatibility with
versions of simplejson earlier than 2.1.0, an integer is also accepted
and is converted to a string with that many spaces.
If specified, *separators* should be an
``(item_separator, key_separator)`` tuple. The default is
``(', ', ': ')`` if *indent* is ``None`` and ``(',', ': ')``
otherwise. To get the most compact JSON representation,
you should specify ``(',', ':')`` to eliminate whitespace.
If *encoding* is not ``None``, then all input :class:`bytes` objects in
Python 3 and 8-bit strings in Python 2 will be transformed
into unicode using that encoding prior to JSON-encoding. The default is
``'utf-8'``. If *encoding* is ``None``, then all :class:`bytes` objects
will be passed to the *default* function in Python 3
.. versionchanged:: 3.15.0
``encoding=None`` disables serializing :class:`bytes` by default in
Python 3.
*default(obj)* is a function that should return a serializable version of
*obj* or raise :exc:`TypeError`. The default implementation always raises
:exc:`TypeError`.
To use a custom :class:`JSONEncoder` subclass (e.g. one that overrides the
:meth:`default` method to serialize additional types), specify it with the
*cls* kwarg.
.. note::
Subclassing is not recommended. Use the *default* kwarg
or *for_json* instead. This is faster and more portable.
If *use_decimal* is true (default: ``True``) then :class:`decimal.Decimal`
will be natively serialized to JSON with full precision.
If *namedtuple_as_object* is true (default: ``True``),
objects with ``_asdict()`` methods will be encoded
as JSON objects.
If *tuple_as_array* is true (default: ``True``),
:class:`tuple` (and subclasses) will be encoded as JSON arrays.
If *iterable_as_array* is true (default: ``False``),
any object not in the above table that implements ``__iter__()``
will be encoded as a JSON array.
.. versionchanged:: 3.8.0
*iterable_as_array* is new in 3.8.0.
If *bigint_as_string* is true (default: ``False``), :class:`int` ``2**53``
and higher or lower than ``-2**53`` will be encoded as strings. This is to
avoid the rounding that happens in Javascript otherwise. Note that this
option loses type information, so use with extreme caution.
See also *int_as_string_bitcount*.
If *sort_keys* is true (not the default), then the output of dictionaries
will be sorted by key; this is useful for regression tests to ensure that
JSON serializations can be compared on a day-to-day basis.
If *item_sort_key* is a callable (not the default), then the output of
dictionaries will be sorted with it. The callable will be used like this:
``sorted(dct.items(), key=item_sort_key)``. This option takes precedence
over *sort_keys*.
If *for_json* is true (not the default), objects with a ``for_json()``
method will use the return value of that method for encoding as JSON
instead of the object.
If *ignore_nan* is true (default: ``False``), then out of range
:class:`float` values (``nan``, ``inf``, ``-inf``) will be serialized as
``null`` in compliance with the ECMA-262 specification. If true, this will
override *allow_nan*.
If *int_as_string_bitcount* is a positive number ``n`` (default: ``None``),
:class:`int` ``2**n`` and higher or lower than ``-2**n`` will be encoded as strings. This is to
avoid the rounding that happens in Javascript otherwise. Note that this
option loses type information, so use with extreme caution.
See also *bigint_as_string* (which is equivalent to `int_as_string_bitcount=53`).
.. note::
JSON is not a framed protocol so unlike :mod:`pickle` or :mod:`marshal` it
does not make sense to serialize more than one JSON document without some
container protocol to delimit them.
.. function:: load(fp, encoding='utf-8', cls=None, object_hook=None, \
parse_float=None, parse_int=None, \
parse_constant=None, object_pairs_hook=None, \
use_decimal=None, **kw)
Deserialize *fp* (a ``.read()``-supporting file-like object containing a JSON
document) to a Python object using this
:ref:`conversion table <json-to-py-table>`. :exc:`JSONDecodeError` will be
raised if the given JSON document is not valid.
If *fp.read()* returns :class:`bytes`, such as a file opened in binary mode,
then an appropriate *encoding* should be specified (the default is UTF-8).
.. note::
:func:`load` will read the rest of the file-like object as a string and
then call :func:`loads`. It does not stop at the end of the first valid
JSON document it finds and it will raise an error if there is anything
other than whitespace after the document. Except for files containing
only one JSON document, it is recommended to use :func:`loads`.
.. note::
In Python 2, :class:`str` is considered to be :class:`bytes` and this
is the default behavior of all :class:`file` objects. If the contents
of *fp* are encoded with an ASCII based encoding other than UTF-8
(e.g. latin-1), then an appropriate *encoding* name must be specified.
Encodings that are not ASCII based (such as UCS-2) are not allowed,
and should be wrapped with ``codecs.getreader(fp)(encoding)``, or
decoded to a :class:`unicode` object and passed to :func:`loads`.
The default setting of ``'utf-8'`` is fastest and should be using
whenever possible.
If *fp.read()* returns :class:`str` then decoded JSON strings that
contain only ASCII characters may be parsed as :class:`str` for
performance and memory reasons. If your code expects only
:class:`unicode` the appropriate solution is to wrap fp with a
reader as demonstrated above.
See :func:`loads` for a description of each argument. The only difference
is that this function reads the JSON document from a file-like object *fp*
instead of a :class:`str` or :class:`bytes`.
.. function:: loads(s, encoding='utf-8', cls=None, object_hook=None, \
parse_float=None, parse_int=None, \
parse_constant=None, object_pairs_hook=None, \
use_decimal=None, **kw)
Deserialize *s* (a :class:`str` or :class:`unicode` instance containing a JSON
document) to a Python object. :exc:`JSONDecodeError` will be
raised if the given JSON document is not valid.
.. note::
In Python 2, :class:`str` is considered to be :class:`bytes` as above,
if your JSON is using an encoding that is not ASCII based, then you must
decode to :class:`unicode` first.
If *s* is a :class:`str` instance and is encoded with an ASCII based encoding
other than UTF-8 (e.g. latin-1), then an appropriate *encoding* name must be
specified. Encodings that are not ASCII based (such as UCS-2) are not
allowed and should be decoded to :class:`unicode` first. Additionally,
decoded JSON strings that contain only ASCII characters may be parsed as
:class:`str` instead of :class:`unicode` for performance and memory
reasons. If your code expects only :class:`unicode` the appropriate
solution is decode *s* to :class:`unicode` prior to calling :func:`loads`.
*object_hook* is an optional function that will be called with the result of
any object literal decode (a :class:`dict`). The return value of
*object_hook* will be used instead of the :class:`dict`. This feature can be used
to implement custom decoders (e.g. `JSON-RPC <http://www.jsonrpc.org>`_
class hinting).
*object_pairs_hook* is an optional function that will be called with the
result of any object literal decode with an ordered list of pairs. The
return value of *object_pairs_hook* will be used instead of the
:class:`dict`. This feature can be used to implement custom decoders that
rely on the order that the key and value pairs are decoded (for example,
:class:`collections.OrderedDict` will remember the order of insertion). If
*object_hook* is also defined, the *object_pairs_hook* takes priority.
*parse_float*, if specified, will be called with the string of every JSON
float to be decoded. By default, this is equivalent to ``float(num_str)``.
This can be used to use another datatype or parser for JSON floats
(e.g. :class:`decimal.Decimal`).
*parse_int*, if specified, will be called with the string of every JSON int
to be decoded. By default, this is equivalent to ``int(num_str)``. This can
be used to use another datatype or parser for JSON integers
(e.g. :class:`float`).
*parse_constant*, if specified, will be called with one of the following
strings: ``'-Infinity'``, ``'Infinity'``, ``'NaN'``. This can be used to
raise an exception if invalid JSON numbers are encountered.
If *use_decimal* is true (default: ``False``) then *parse_float* is set to
:class:`decimal.Decimal`. This is a convenience for parity with the
:func:`dump` parameter.
If *iterable_as_array* is true (default: ``False``),
any object not in the above table that implements ``__iter__()``
will be encoded as a JSON array.
.. versionchanged:: 3.8.0
*iterable_as_array* is new in 3.8.0.
To use a custom :class:`JSONDecoder` subclass, specify it with the ``cls``
kwarg. Additional keyword arguments will be passed to the constructor of the
class. You probably shouldn't do this.
.. note::
Subclassing is not recommended. You should use *object_hook* or
*object_pairs_hook*. This is faster and more portable than subclassing.
.. exception:: JSONDecodeError(msg, doc, pos, end=None)
Subclass of :exc:`ValueError` with the following additional attributes:
.. attribute:: msg
The unformatted error message
.. attribute:: doc
The JSON document being parsed
.. attribute:: pos
The start index of doc where parsing failed
.. attribute:: end
The end index of doc where parsing failed (may be ``None``)
.. attribute:: lineno
The line corresponding to pos
.. attribute:: colno
The column corresponding to pos
.. attribute:: endlineno
The line corresponding to end (may be ``None``)
.. attribute:: endcolno
The column corresponding to end (may be ``None``)
The JSON format is specified by RFC 7159 and by ECMA-404. This section details this module's level of compliance with the RFC. For simplicity, :class:`JSONEncoder` and :class:`JSONDecoder` subclasses, and parameters other than those explicitly mentioned, are not considered.
This module does not comply with the RFC in a strict fashion, implementing some extensions that are valid JavaScript but not valid JSON. In particular:
- Infinite and NaN number values are accepted and output;
- Repeated names within an object are accepted, and only the value of the last name-value pair is used.
Since the RFC permits RFC-compliant parsers to accept input texts that are not RFC-compliant, this module's deserializer is technically RFC-compliant under default settings.
The RFC recommends that JSON be represented using either UTF-8, UTF-16, or UTF-32, with UTF-8 being the recommended default for maximum interoperability.
As permitted, though not required, by the RFC, this module's serializer sets ensure_ascii=True by default, thus escaping the output so that the resulting strings only contain ASCII characters.
Other than the ensure_ascii parameter, this module is defined strictly in terms of conversion between Python objects and :class:`Unicode strings <str>`, and thus does not otherwise directly address the issue of character encodings.
The RFC prohibits adding a byte order mark (BOM) to the start of a JSON text, and this module's serializer does not add a BOM to its output. The RFC permits, but does not require, JSON deserializers to ignore an initial BOM in their input. This module's deserializer will ignore an initial BOM, if present.
The RFC does not explicitly forbid JSON strings which contain byte sequences that don't correspond to valid Unicode characters (e.g. unpaired UTF-16 surrogates), but it does note that they may cause interoperability problems. By default, this module accepts and outputs (when present in the original :class:`str`) codepoints for such sequences.
The RFC does not permit the representation of infinite or NaN number values.
Despite that, by default, this module accepts and outputs Infinity,
-Infinity, and NaN as if they were valid JSON number literal values:
>>> # Neither of these calls raises an exception, but the results are not valid JSON
>>> json.dumps(float('-inf'))
'-Infinity'
>>> json.dumps(float('nan'))
'NaN'
>>> # Same when deserializing
>>> json.loads('-Infinity')
-inf
>>> json.loads('NaN')
nanIn the serializer, the allow_nan parameter can be used to alter this behavior. In the deserializer, the parse_constant parameter can be used to alter this behavior.
The RFC specifies that the names within a JSON object should be unique, but does not mandate how repeated names in JSON objects should be handled. By default, this module does not raise an exception; instead, it ignores all but the last name-value pair for a given name:
>>> weird_json = '{"x": 1, "x": 2, "x": 3}'
>>> json.loads(weird_json) == {'x': 3}
TrueThe object_pairs_hook parameter can be used to alter this behavior.
The old version of JSON specified by the obsolete RFC 4627 required that the top-level value of a JSON text must be either a JSON object or array (Python :class:`dict` or :class:`list`), and could not be a JSON null, boolean, number, or string value. RFC 7159 removed that restriction, and this module does not and has never implemented that restriction in either its serializer or its deserializer.
Regardless, for maximum interoperability, you may wish to voluntarily adhere to the restriction yourself.
Some JSON deserializer implementations may set limits on:
- the size of accepted JSON texts
- the maximum level of nesting of JSON objects and arrays
- the range and precision of JSON numbers
- the content and maximum length of JSON strings
This module does not impose any such limits beyond those of the relevant Python datatypes themselves or the Python interpreter itself.
When serializing to JSON, beware any such limitations in applications that may consume your JSON. In particular, it is common for JSON numbers to be deserialized into IEEE 754 double precision numbers and thus subject to that representation's range and precision limitations. This is especially relevant when serializing Python :class:`int` values of extremely large magnitude, or when serializing instances of "exotic" numerical types such as :class:`decimal.Decimal`.
The :mod:`simplejson.tool` module provides a simple command line interface to validate and pretty-print JSON.
If the optional :option:`infile` and :option:`outfile` arguments are not specified, :attr:`sys.stdin` and :attr:`sys.stdout` will be used respectively:
$ echo '{"json": "obj"}' | python -m simplejson.tool
{
"json": "obj"
}
$ echo '{1.2:3.4}' | python -m simplejson.tool
Expecting property name enclosed in double quotes: line 1 column 2 (char 1).. cmdoption:: infile
The JSON file to be validated or pretty-printed::
$ python -m simplejson.tool mp_films.json
[
{
"title": "And Now for Something Completely Different",
"year": 1971
},
{
"title": "Monty Python and the Holy Grail",
"year": 1975
}
]
If *infile* is not specified, read from :attr:`sys.stdin`.
.. cmdoption:: outfile
Write the output of the *infile* to the given *outfile*. Otherwise, write it
to :attr:`sys.stdout`.
Footnotes
| [1] | As noted in the errata for RFC 7159, JSON permits literal U+2028 (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR) characters in strings, whereas JavaScript (as of ECMAScript Edition 5.1) does not. |