json
Bob Ippolito <bob@redivi.com>
Bob Ippolito <bob@redivi.com>
Source code: Lib/json/__init__.py
import json from json import AttrDict
JSON (JavaScript Object Notation), specified by 7159
(which obsoletes 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 JavaScript1 ).
Warning
Be cautious when parsing JSON data from untrusted sources. A malicious JSON string may cause the decoder to consume considerable CPU and memory resources. Limiting the size of data to be parsed is recommended.
json
exposes an API familiar to users of the standard library marshal
and pickle
modules.
Encoding basic Python object hierarchies:
>>> import 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('\u1234'))
"\u1234"
>>> print(json.dumps('\\'))
"\\"
>>> print(json.dumps({"c": 0, "b": 0, "a": 0}, sort_keys=True))
{"a": 0, "b": 0, "c": 0}
>>> from io import StringIO
>>> io = StringIO()
>>> json.dump(['streaming API'], io)
>>> io.getvalue()
'["streaming API"]'
Compact encoding:
>>> import json
>>> json.dumps([1, 2, 3, {'4': 5, '6': 7}], separators=(',', ':'))
'[1,2,3,{"4":5,"6":7}]'
Pretty printing:
>>> import json
>>> print(json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4))
{
"4": 5,
"6": 7
}
Decoding JSON:
>>> import json
>>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]')
['foo', {'bar': ['baz', None, 1.0, 2]}]
>>> json.loads('"\\"foo\\bar"')
'"foo\x08ar'
>>> from io import StringIO
>>> io = StringIO('["streaming API"]')
>>> json.load(io)
['streaming API']
Specializing JSON object decoding:
>>> import 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('1.1')
Extending JSONEncoder
:
>>> import json
>>> class ComplexEncoder(json.JSONEncoder):
... def default(self, obj):
... if isinstance(obj, complex):
... return [obj.real, obj.imag]
... # Let the base class default method raise the TypeError
... return json.JSONEncoder.default(self, obj)
...
>>> json.dumps(2 + 1j, cls=ComplexEncoder)
'[2.0, 1.0]'
>>> ComplexEncoder().encode(2 + 1j)
'[2.0, 1.0]'
>>> list(ComplexEncoder().iterencode(2 + 1j))
['[2.0', ', 1.0', ']']
Using json.tool
from the shell to validate and pretty-print:
$ echo '{"json":"obj"}' | python -m json.tool
{
"json": "obj"
}
$ echo '{1.2:3.4}' | python -m json.tool
Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
See json-commandline
for detailed documentation.
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.
Note
This module's encoders and decoders preserve input and output order by default. Order is only lost if the underlying containers are unordered.
dump(obj, fp, , skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, default=None, sort_keys=False,*kw)
Serialize obj as a JSON formatted stream to fp (a .write()
-supporting file-like object
) using this conversion table
<py-to-json-table>
.
If skipkeys is true (default: False
), then dict keys that are not of a basic type (str
, int
, float
, bool
, None
) will be skipped instead of raising a TypeError
.
The json
module always produces str
objects, not bytes
objects. Therefore, fp.write()
must support str
input.
If ensure_ascii is true (the default), the output is guaranteed to have all incoming non-ASCII characters escaped. If ensure_ascii is false, these characters will be output as-is.
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 a RecursionError
(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 JSON specification. If allow_nan is true, their JavaScript equivalents (NaN
, Infinity
, -Infinity
) will be used.
If indent is a non-negative integer or string, then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0, negative, or ""
will only insert newlines. None
(the default) selects the most compact representation. Using a positive integer indent indents that many spaces per level. If indent is a string (such as "\t"
), that string is used to indent each level.
3.2 Allow strings for indent in addition to integers.
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.
3.4 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 not specified, TypeError
is raised.
If sort_keys is true (default: False
), then the output of dictionaries will be sorted by key.
To use a custom JSONEncoder
subclass (e.g. one that overrides the default
method to serialize additional types), specify it with the cls kwarg; otherwise JSONEncoder
is used.
3.6 All optional parameters are now keyword-only <keyword-only_parameter>
.
Note
Unlike pickle
and marshal
, JSON is not a framed protocol, so trying to serialize multiple objects with repeated calls to dump
using the same fp will result in an invalid JSON file.
dumps(obj, , skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, default=None, sort_keys=False,*kw)
Serialize obj to a JSON formatted str
using this conversion
table <py-to-json-table>
. The arguments have the same meaning as in dump
.
Note
Keys in key/value pairs of JSON are always of the type str
. When a dictionary is converted into JSON, all the keys of the dictionary are coerced to strings. As a result of this, if a dictionary is converted into JSON and then back into a dictionary, the dictionary may not equal the original one. That is, loads(dumps(x)) != x
if x has non-string keys.
load(fp, , cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None,*kw)
Deserialize fp (a .read()
-supporting text file
or binary file
containing a JSON document) to a Python object using this conversion table <json-to-py-table>
.
object_hook is an optional function that will be called with the result of any object literal decoded (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 decoded 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. If object_hook is also defined, the object_pairs_hook takes priority.
3.1 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
).
3.12 The default parse_int of int
now limits the maximum length of the integer string via the interpreter's integer string
conversion length limitation <int_max_str_digits>
to help avoid denial of service attacks.
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.
3.1 parse_constant doesn't get called on 'null', 'true', 'false' anymore.
To use a custom JSONDecoder
subclass, specify it with the cls
kwarg; otherwise JSONDecoder
is used. Additional keyword arguments will be passed to the constructor of the class.
If the data being deserialized is not a valid JSON document, a JSONDecodeError
will be raised.
3.6 All optional parameters are now keyword-only <keyword-only_parameter>
.
3.6 fp can now be a binary file
. The input encoding should be UTF-8, UTF-16 or UTF-32.
loads(s, , cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None,*kw)
Deserialize s (a str
, bytes
or bytearray
instance containing a JSON document) to a Python object using this conversion table <json-to-py-table>
.
The other arguments have the same meaning as in load
.
If the data being deserialized is not a valid JSON document, a JSONDecodeError
will be raised.
3.6 s can now be of type bytes
or bytearray
. The input encoding should be UTF-8, UTF-16 or UTF-32.
3.9 The keyword argument encoding has been removed.
Simple JSON decoder.
Performs the following translations in decoding by default:
JSON | Python |
---|---|
object | dict |
array | list |
string | str |
number (int) | int |
number (real) | float |
true | True |
false | False |
null | None |
It also understands NaN
, Infinity
, and -Infinity
as their corresponding float
values, which is outside the JSON spec.
object_hook, if specified, 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, if specified will be called with the result of every JSON object decoded 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. If object_hook is also defined, the object_pairs_hook takes priority.
3.1 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 strict is false (True
is the default), then control characters will be allowed inside strings. Control characters in this context are those with character codes in the 0--31 range, including '\t'
(tab), '\n'
, '\r'
and '\0'
.
If the data being deserialized is not a valid JSON document, a JSONDecodeError
will be raised.
3.6 All parameters are now keyword-only <keyword-only_parameter>
.
decode(s)
Return the Python representation of s (a str
instance containing a JSON document).
JSONDecodeError
will be raised if the given JSON document is not valid.
raw_decode(s)
Decode a JSON document from s (a str
beginning with a JSON document) 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.
Extensible JSON encoder for Python data structures.
Supports the following objects and types by default:
Python | JSON |
---|---|
dict | object |
list, tuple | array |
str | string |
int, float, int- & float-derived Enums | number |
True | true |
False | false |
None | null |
3.4 Added support for int- and float-derived Enum classes.
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
).
If skipkeys is false (the default), a TypeError
will be raised when trying to encode keys that are not str
, int
, float
or None
. If skipkeys is true, such items are simply skipped.
If ensure_ascii is true (the default), the output is guaranteed to have all incoming non-ASCII characters escaped. If ensure_ascii is false, these characters will be output as-is.
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 a RecursionError
). 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.
If sort_keys is true (default: False
), 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 indent is a non-negative integer or string, then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0, negative, or ""
will only insert newlines. None
(the default) selects the most compact representation. Using a positive integer indent indents that many spaces per level. If indent is a string (such as "\t"
), that string is used to indent each level.
3.2 Allow strings for indent in addition to integers.
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.
3.4 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 not specified, TypeError
is raised.
3.6 All parameters are now keyword-only <keyword-only_parameter>
.
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)
# Let the base class default method raise the TypeError
return json.JSONEncoder.default(self, o)
encode(o)
Return a JSON string representation of a Python data structure, o. For example:
>>> 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 json.JSONEncoder().iterencode(bigobject):
mysocket.write(chunk)
JSONDecodeError(msg, doc, pos)
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.
lineno
The line corresponding to pos.
colno
The column corresponding to pos.
3.5
Subclass of dict
object that also supports attribute style dotted access.
This class is intended for use with the object_hook
in json.load
and json.loads
:
.. doctest::
>>> json_string = '{"mercury": 88, "venus": 225, "earth": 365, "mars": 687}' >>> orbital_period = json.loads(json_string, object_hook=AttrDict) >>> orbital_period['earth'] # Dict style lookup 365 >>> orbital_period.earth # Attribute style lookup 365 >>> orbital_period.keys() # All dict methods are present dict_keys(['mercury', 'venus', 'earth', 'mars'])
Attribute style access only works for keys that are valid attribute names. In contrast, dictionary style access works for all keys. For example, d.two words
contains a space and is not syntactically valid Python, so d["two words"]
should be used instead.
If a key has the same name as a dictionary method, then a dictionary lookup finds the key and an attribute lookup finds the method:
>>> d = AttrDict(items=50) >>> d['items'] # Lookup the key 50 >>> d.items() # Call the method dict_items([('items', 50)])
3.12
The JSON format is specified by 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.
The RFC requires 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 <str>
, and thus does not otherwise directly address the issue of character encodings.
The RFC prohibits adding a byte order mark (BOM) to the start of a JSON text, and this module's serializer does not add a BOM to its output. The RFC permits, but does not require, JSON deserializers to ignore an initial BOM in their input. This module's deserializer raises a 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
) code points for such sequences.
The RFC does not permit the representation of infinite or NaN number values. Despite that, by default, this module accepts and outputs Infinity
, -Infinity
, and NaN
as if they were valid JSON number literal values:
>>> # Neither of these calls raises an exception, but the results are not valid JSON
>>> json.dumps(float('-inf'))
'-Infinity'
>>> json.dumps(float('nan'))
'NaN'
>>> # Same when deserializing
>>> json.loads('-Infinity')
-inf
>>> json.loads('NaN')
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.
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}
The object_pairs_hook parameter can be used to alter this behavior.
The old version of JSON specified by the obsolete 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. 7159
removed that restriction, and this module does not and has never implemented that restriction in either its serializer or its deserializer.
Regardless, for maximum interoperability, you may wish to voluntarily adhere to the restriction yourself.
Some JSON deserializer implementations may set limits on:
- the size of accepted JSON texts
- the maximum level of nesting of JSON objects and arrays
- the range and precision of JSON numbers
- the content and maximum length of JSON strings
This module does not impose any such limits beyond those of the relevant Python datatypes themselves or the Python interpreter itself.
When serializing to JSON, beware any such limitations in applications that may consume your JSON. In particular, it is common for JSON numbers to be deserialized into IEEE 754 double precision numbers and thus subject to that representation's range and precision limitations. This is especially relevant when serializing Python int
values of extremely large magnitude, or when serializing instances of "exotic" numerical types such as decimal.Decimal
.
json.tool
Source code: Lib/json/tool.py
The json.tool
module provides a simple command line interface to validate and pretty-print JSON objects.
If the optional infile
and outfile
arguments are not specified, sys.stdin
and sys.stdout
will be used respectively:
$ echo '{"json": "obj"}' | python -m json.tool
{
"json": "obj"
}
$ echo '{1.2:3.4}' | python -m json.tool
Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
3.5 The output is now in the same order as the input. Use the --sort-keys
option to sort the output of dictionaries alphabetically by key.
infile
The JSON file to be validated or pretty-printed:
$ python -m json.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
.
--sort-keys
Sort the output of dictionaries alphabetically by key.
3.5
--no-ensure-ascii
Disable escaping of non-ascii characters, see json.dumps
for more information.
3.9
--json-lines
Parse every input line as separate JSON object.
3.8
--indent, --tab, --no-indent, --compact
Mutually exclusive options for whitespace control.
3.9
-h, --help
Show the help message.
Footnotes
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.↩