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 exposes an API familiar to users of the standard library marshal and pickle modules. It is the externally maintained version of the json library contained in Python 2.6, but maintains compatibility with Python 2.5 and (currently) has significant performance advantages, even without using the optional C extension for speedups. simplejson is also supported on Python 3.3+.

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 = [u'foo', {u'bar': [u'baz', None, 1.0, 2]}]
>>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]') == obj
True
True
>>> from simplejson.compat import StringIO
>>> io = StringIO('["streaming API"]')
True


>>> import simplejson as json
>>> from decimal import Decimal
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
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)


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.

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

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

If ensure_ascii is false (default: True), then 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.

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.

Changed in version 2.1.0: Changed indent from an integer number of spaces to a string.

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.

Changed in version 2.1.4: Use (',', ': ') as default if indent is not None.

encoding is the character encoding for str instances, default is 'utf-8'.

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

Changed in version 2.1.0: use_decimal is new in 2.1.0.

Changed in version 2.2.0: The default of use_decimal changed to True in 2.2.0.

If namedtuple_as_object is true (default: True), objects with _asdict() methods will be encoded as JSON objects.

Changed in version 2.2.0: namedtuple_as_object is new in 2.2.0.

Changed in version 2.3.0: namedtuple_as_object no longer requires that these objects be subclasses of tuple.

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.

Changed in version 2.2.0: tuple_as_array is new in 2.2.0.

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.

Changed in version 2.4.0: bigint_as_string is new in 2.4.0.

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.

Changed in version 3.0.0: Sorting now happens after the keys have been coerced to strings, to avoid comparison of heterogeneously typed objects (since this does not work in Python 3.3+)

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.

Changed in version 2.5.0: item_sort_key is new in 2.5.0.

Changed in version 3.0.0: Sorting now happens after the keys have been coerced to strings, to avoid comparison of heterogeneously typed objects (since this does not work in Python 3.3+)

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.

Changed in version 3.2.0: for_json is new in 3.2.0.

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.

Changed in version 3.2.0: ignore_nan is new in 3.2.0.

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).

Changed in version 3.5.0: int_as_string_bitcount is new in 3.5.0.

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.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 ensure_ascii is false, then the return value will be a unicode instance. The other arguments have the same meaning as in dump(). Note that the default ensure_ascii setting has much better performance in Python 2.

The other options have the same meaning as in dump().

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 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 simply 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.

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.

Changed in version 2.1.0: Added support for object_pairs_hook.

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.

Changed in version 2.1.0: use_decimal is new in 2.1.0.

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.

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().

simplejson.loads(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 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.

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.

If s is a 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 decode s to unicode prior to calling loads.

The other arguments have the same meaning as in load().

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.

Changed in version 2.1.0: Added support for object_pairs_hook.

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 s (a str or unicode instance containing a JSON document)

If s is a 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 decode s to unicode prior to calling decode.

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

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.

Changed in version 2.2.0: Changed namedtuple encoding from JSON array to object.

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.

Changed in version 3.0.0: Sorting now happens after the keys have been coerced to strings, to avoid comparison of heterogeneously typed objects (since this does not work in Python 3.3+)

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.

Changed in version 2.5.0: item_sort_key is new in 2.5.0.

Changed in version 3.0.0: Sorting now happens after the keys have been coerced to strings, to avoid comparison of heterogeneously typed objects (since this does not work in Python 3.3+)

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.

Changed in version 2.1.0: Changed indent from an integer number of spaces to a string.

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.

Changed in version 2.1.4: Use (',', ': ') as default if indent is not None.

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 strings will be transformed into unicode using that encoding prior to JSON-encoding. The default is 'utf-8'.

If namedtuple_as_object is true (default: True), objects with _asdict() methods will be encoded as JSON objects.

Changed in version 2.2.0: namedtuple_as_object is new in 2.2.0.

Changed in version 2.3.0: namedtuple_as_object no longer requires that these objects be subclasses of tuple.

If tuple_as_array is true (default: True), tuple (and subclasses) will be encoded as JSON arrays.

Changed in version 2.2.0: tuple_as_array is new in 2.2.0.

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.

Changed in version 2.4.0: bigint_as_string is new in 2.4.0.

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.

Changed in version 3.2.0: for_json is new in 3.2.0.

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.

Changed in version 3.2.0: ignore_nan is new in 3.2.0.

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.

Changed in version 2.1.0: New in 2.1.0

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.

Changed in version 3.6.0: Older versions would raise ValueError when an initial BOM is 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
-inf
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}'
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.