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=False, 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 producestr
objects in Python 3, notbytes
objects. Therefore,fp.write()
must supportstr
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 Pythonstr
tounicode
coercion rules. Unlessfp.write()
explicitly understandsunicode
(as incodecs.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=False, 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 aTypeError
.Note
When using Python 2, both
str
andunicode
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 astr
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 anOverflowError
(or worse).If allow_nan is false (default:
False
), then it will be aValueError
to serialize out of rangefloat
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.Changed in version 3.19.0: The default for allow_nan was changed to False for better spec compliance.
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 isNone
and(',', ': ')
otherwise. To get the most compact JSON representation, you should specify(',', ':')
to eliminate whitespace.If encoding is not
None
, then all inputbytes
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 isNone
, then allbytes
objects will be passed to the default function in Python 3Changed in version 3.15.0:
encoding=None
disables serializingbytes
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 raisesTypeError
.To use a custom
JSONEncoder
subclass (e.g. one that overrides thedefault()
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
) thendecimal.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 rangefloat
values (nan
,inf
,-inf
) will be serialized asnull
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
ormarshal
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, allow_nan=False, **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 callloads()
. 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 useloads()
.Note
In Python 2,
str
is considered to bebytes
and this is the default behavior of allfile
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 withcodecs.getreader(fp)(encoding)
, or decoded to aunicode
object and passed toloads()
. 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 asstr
for performance and memory reasons. If your code expects onlyunicode
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 astr
orbytes
.
- 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, allow_nan=False, **kw)¶
Deserialize s (a
str
orunicode
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 bebytes
as above, if your JSON is using an encoding that is not ASCII based, then you must decode tounicode
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 tounicode
first. Additionally, decoded JSON strings that contain only ASCII characters may be parsed asstr
instead ofunicode
for performance and memory reasons. If your code expects onlyunicode
the appropriate solution is decode s tounicode
prior to callingloads()
.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 thedict
. 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
).Changed in version 3.19.0: The integer to string conversion length limitation introduced in Python 3.11 has been backported. An attempt to parse an integer with more than 4300 digits will result in an exception unless a suitable alternative parser is specified (e.g.
decimal.Decimal
)If use_decimal is true (default:
False
) then parse_float is set todecimal.Decimal
. This is a convenience for parity with thedump()
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 thecls
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.
allow_nan, if True (default false), will allow the parser to accept the non-standard floats
NaN
,Infinity
, and-Infinity
.Changed in version 3.19.0: This argument was added to make it possible to use the legacy behavior now that the parser is more strict about compliance to the standard.
parse_constant, if specified, will be called with one of the following strings:
'-Infinity'
,'Infinity'
,'NaN'
. It is not recommended to use this feature, as it is rare to parse non-compliant JSON containing these values.
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, allow_nan=False)¶
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
When allow_nan is True, it also understands
NaN
,Infinity
, and-Infinity
as their correspondingfloat
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 decodingunicode
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
).Changed in version 3.19.0: The integer to string conversion length limitation introduced in Python 3.11 has been backported. An attempt to parse an integer with more than 4300 digits will result in an exception unless a suitable alternative parser is specified (e.g.
decimal.Decimal
)parse_constant, if specified, will be called with one of the following strings:
'-Infinity'
,'Infinity'
,'NaN'
. It is not recommended to use this feature, as it is rare to parse non-compliant JSON containing these values.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, ifFalse
then control characters will be allowed in strings.allow_nan when True (not the default), the decoder will allow
NaN
,Infinity
, and-Infinity
as their corresponding floats.Changed in version 3.19.0: This argument was added to make it behave closer to the spec by default. The previous behavior can be restored by setting this to False.
- 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
orunicode
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=False, 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.
When allow_nan is True, it also understands
NaN
,Infinity
, and-Infinity
as their correspondingfloat
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 foro
if possible, otherwise it should call the superclass implementation (to raiseTypeError
).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 (not the default), then
NaN
,Infinity
, and-Infinity
will be encoded as such. This behavior is not JSON specification compliant. Otherwise, it will be aValueError
to encode such floats. See also ignore_nan for ECMA-262 compliant behavior.Changed in version 3.19.0: This default is now False to make it behave closer to the spec. The previous behavior can be restored by setting this to False.
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 isNone
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 inputbytes
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 isNone
, then allbytes
objects will be passed to thedefault()
method in Python 3Changed in version 3.15.0:
encoding=None
disables serializingbytes
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 afor_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 rangefloat
values (nan
,inf
,-inf
) will be serialized asnull
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 thaniterencode()
.
- class simplejson.JSONEncoderForHTML(skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=False, 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
if the allow_nan flag is enabled:
>>> # Neither of these calls raises an exception, but the results are not valid JSON
>>> json.dumps(float('-inf'), allow_nan=True)
'-Infinity'
>>> json.dumps(float('nan'), allow_nan=True)
'NaN'
>>> # Same when deserializing
>>> json.loads('-Infinity', allow_nan=True)
-inf
>>> json.loads('NaN', allow_nan=True)
nan
>>> # ignore_nan uses the ECMA-262 behavior to serialize these as null
>>> json.dumps(float('-inf'), ignore_nan=True)
'null'
>>> json.dumps(float('nan'), ignore_nan=True)
'null'
In the serializer, the allow_nan parameter can be used to alter this behavior. In the deserializer, the allow_nan and parse_constant parameters 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