simplejson — JSON encoder and decoder

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] ).

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.

simplejson exposes an API familiar to users of the standard library marshal and pickle modules. It is the externally maintained version of the 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'
True

Using 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'
True

Specializing 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')
True

Specializing 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 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'))
6

Serializing 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.

Basic Usage

simplejson.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 conversion table.

The simplejson module will produce str objects in Python 3, not bytes objects. Therefore, fp.write() must support str input.

See 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 unicode instances, subject to normal Python str to unicode coercion rules. Unless fp.write() explicitly understands unicode (as in 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.

simplejson.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 str.

If skipkeys is true (default: False), then dict keys that are not of a basic type (str, int, long, float, bool, None) will be skipped instead of raising a TypeError.

Note

When using Python 2, both str and 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 unicode object. By default, as a memory optimization, the result would be a 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 OverflowError (or worse).

If allow_nan is false (default: True), then it will be a ValueError to serialize out of range 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 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 bytes objects will be passed to the default function in Python 3

Changed in version 3.15.0: encoding=None disables serializing bytes by default in Python 3.

default(obj) is a function that should return a serializable version of obj or raise TypeError. The default implementation always raises TypeError.

To use a custom JSONEncoder subclass (e.g. one that overrides the 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 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), 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.

Changed in version 3.8.0: iterable_as_array is new in 3.8.0.

If bigint_as_string is true (default: False), 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 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), 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 pickle or marshal it does not make sense to serialize more than one JSON document without some container protocol to delimit them.

simplejson.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 conversion table. JSONDecodeError will be raised if the given JSON document is not valid.

If fp.read() returns bytes, such as a file opened in binary mode, then an appropriate encoding should be specified (the default is UTF-8).

Note

load() will read the rest of the file-like object as a string and then call 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 loads().

Note

In Python 2, str is considered to be bytes and this is the default behavior of all 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 unicode object and passed to loads(). The default setting of 'utf-8' is fastest and should be using whenever possible.

If fp.read() returns str then decoded JSON strings that contain only ASCII characters may be parsed as str for performance and memory reasons. If your code expects only unicode the appropriate solution is to wrap fp with a reader as demonstrated above.

See 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 str or bytes.

simplejson.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 str or unicode instance containing a JSON document) to a Python object. JSONDecodeError will be raised if the given JSON document is not valid.

Note

In Python 2, str is considered to be bytes as above, if your JSON is using an encoding that is not ASCII based, then you must decode to unicode first.

If s is a 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 unicode first. Additionally, decoded JSON strings that contain only ASCII characters may be parsed as str instead of unicode for performance and memory reasons. If your code expects only unicode the appropriate solution is decode s to unicode prior to calling loads().

object_hook is an optional function that will be called with the result of any object literal decode (a dict). The return value of object_hook will be used instead of the dict. This feature can be used to implement custom decoders (e.g. JSON-RPC 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 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, 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. 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. 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 decimal.Decimal. This is a convenience for parity with the 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.

Changed in version 3.8.0: iterable_as_array is new in 3.8.0.

To use a custom 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.

Encoders and decoders

class simplejson.JSONDecoder(encoding='utf-8', object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, strict=True)

Simple JSON decoder.

Performs the following translations in decoding by default:

JSON	Python 2	Python 3
object	dict	dict
array	list	list
string	unicode	str
number (int)	int, long	int
number (real)	float	float
true	True	True
false	False	False
null	None	None

It also understands NaN, Infinity, and -Infinity as their corresponding float values, which is outside the JSON spec.

encoding determines the encoding used to interpret any str objects decoded by this instance ('utf-8' by default). It has no effect when decoding unicode objects.

Note that currently only encodings that are a superset of ASCII work, strings of other encodings should be passed in as unicode.

object_hook is an optional function that will be called with the result of every JSON object decoded and its return value will be used in place of the given dict. This can be used to provide custom deserializations (e.g. to support JSON-RPC 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 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, 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. 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. 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.

strict controls the parser’s behavior when it encounters an invalid control character in a string. The default setting of True means that unescaped control characters are parse errors, if False then control characters will be allowed in strings.

decode(s)

Return the Python representation of the JSON document s. See loads() for details. It is preferable to use that rather than this class.

raw_decode(s[, idx=0])

Decode a JSON document from s (a str or unicode beginning with a JSON document) starting from the index idx and return a 2-tuple of the Python representation and the index in s where the document ended.

This can be used to decode a JSON document from a string that may have extraneous data at the end, or to decode a string that has a series of JSON objects.

JSONDecodeError will be raised if the given JSON document is not valid.

class simplejson.JSONEncoder(skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, encoding='utf-8', default=None, use_decimal=True, namedtuple_as_object=True, tuple_as_array=True, bigint_as_string=False, item_sort_key=None, for_json=True, ignore_nan=False, int_as_string_bitcount=None, iterable_as_array=False)

Extensible JSON encoder for Python data structures.

Supports the following objects and types by default:

Python	JSON
dict, namedtuple	object
list, tuple	array
str, unicode	string
int, long, float	number
True	true
False	false
None	null

Note

The JSON format only permits strings to be used as object keys, thus any Python dicts to be encoded should only have string keys. For backwards compatibility, several other types are automatically coerced to strings: int, long, float, Decimal, bool, and None. It is error-prone to rely on this behavior, so avoid it when possible. Dictionaries with other types used as keys should be pre-processed or wrapped in another type with an appropriate for_json method to transform the keys during encoding.

It also understands NaN, Infinity, and -Infinity as their corresponding float values, which is outside the JSON spec.

To extend this to recognize other objects, subclass and implement a default() method with another method that returns a serializable object for o if possible, otherwise it should call the superclass implementation (to raise TypeError).

Note

Subclassing is not recommended. You should use the default or for_json kwarg. This is faster and more portable than subclassing.

If skipkeys is false (the default), then it is a TypeError to attempt encoding of keys that are not str, int, long, float, Decimal, bool, or None. If skipkeys is true, such items are simply skipped.

If ensure_ascii is true (the default), the output is guaranteed to be str objects with all incoming unicode characters escaped. If ensure_ascii is false, the output will be a unicode object.

If check_circular is true (the default), then lists, dicts, and custom encoded objects will be checked for circular references during encoding to prevent an infinite recursion (which would cause an OverflowError). Otherwise, no such check takes place.

If allow_nan is true (the default), then NaN, Infinity, and -Infinity will be encoded as such. This behavior is not JSON specification compliant, but is consistent with most JavaScript based encoders and decoders. Otherwise, it will be a ValueError to encode such floats. See also ignore_nan for ECMA-262 compliant behavior.

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 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 specified, default should be a function that gets called for objects that can’t otherwise be serialized. It should return a JSON encodable version of the object or raise a TypeError.

If encoding is not None, then all input 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 bytes objects will be passed to the default() method in Python 3

Changed in version 3.15.0: encoding=None disables serializing bytes by default in Python 3.

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), 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.

Changed in version 3.8.0: iterable_as_array is new in 3.8.0.

If bigint_as_string is true (default: False), 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.

If for_json is true (default: False), 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 float values (nan, inf, -inf) will be serialized as null in compliance with the ECMA-262 specification. If true, this will override allow_nan.

default(o)

Implement this method in a subclass such that it returns a serializable object for o, or calls the base implementation (to raise a TypeError).

For example, to support arbitrary iterators, you could implement default like this:

def default(self, o):
    try:
        iterable = iter(o)
    except TypeError:
        pass
    else:
        return list(iterable)
    return JSONEncoder.default(self, o)

Note

Subclassing is not recommended. You should implement this as a function and pass it to the default kwarg of dumps(). This is faster and more portable than subclassing. The semantics are the same, but without the self argument or the call to the super implementation.

encode(o)

Return a JSON string representation of a Python data structure, o. For example:

>>> import simplejson as json
>>> json.JSONEncoder().encode({"foo": ["bar", "baz"]})
'{"foo": ["bar", "baz"]}'

iterencode(o)

Encode the given object, o, and yield each string representation as available. For example:

for chunk in JSONEncoder().iterencode(bigobject):
    mysocket.write(chunk)

Note that encode() has much better performance than iterencode().

class simplejson.JSONEncoderForHTML(skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, encoding='utf-8', default=None, use_decimal=True, namedtuple_as_object=True, tuple_as_array=True, bigint_as_string=False, item_sort_key=None, for_json=True, ignore_nan=False, int_as_string_bitcount=None)

Subclass of JSONEncoder that escapes &, <, and > for embedding in HTML.

It also escapes the characters U+2028 (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR), irrespective of the ensure_ascii setting, as these characters are not valid in JavaScript strings (see http://timelessrepo.com/json-isnt-a-javascript-subset).

Exceptions

exception simplejson.JSONDecodeError(msg, doc, pos, end=None)

Subclass of ValueError with the following additional attributes:

msg

The unformatted error message

doc

The JSON document being parsed

pos

The start index of doc where parsing failed

end

The end index of doc where parsing failed (may be None)

lineno

The line corresponding to pos

colno

The column corresponding to pos

endlineno

The line corresponding to end (may be None)

endcolno

The column corresponding to end (may be None)

Standard Compliance and Interoperability

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, JSONEncoder and 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.

Character Encodings

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 Unicode strings, 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 str) codepoints for such sequences.

Infinite and NaN Number Values

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')
nan

In 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.

Repeated Names Within an Object

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}
True

The object_pairs_hook parameter can be used to alter this behavior.

Top-level Non-Object, Non-Array Values

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 dict or 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.

Implementation Limitations

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 int values of extremely large magnitude, or when serializing instances of “exotic” numerical types such as decimal.Decimal.

Command Line Interface

The simplejson.tool module provides a simple command line interface to validate and pretty-print JSON.

If the optional infile and outfile arguments are not specified, sys.stdin and 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)

Command line options

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 sys.stdin.

outfile

Write the output of the infile to the given outfile. Otherwise, write it to 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.