18.2. json — JSON encoder and decoder — Python v2.7 documentation (original) (raw)

New in version 2.6.

JSON (JavaScript Object Notation) <http://json.org> is a subset of JavaScript syntax (ECMA-262 3rd edition) used as a lightweight data interchange format.

json exposes an API familiar to users of the standard librarymarshal 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(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 StringIO 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]}]') [u'foo', {u'bar': [u'baz', None, 1.0, 2]}] json.loads('"\"foo\bar"') u'"foo\x08ar' from StringIO import StringIO io = StringIO('["streaming API"]') json.load(io) [u'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] ... return json.JSONEncoder.default(self, obj) ... 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 -mjson.tool { "json": "obj" } $ echo '{ 1.2:3.4}' | python -mjson.tool Expecting property name: line 1 column 2 (char 2)

Note

The JSON produced by this module’s default settings is a subset of YAML, so it may be used as a serializer for that as well.

18.2.1. Basic Usage¶

json.dump(obj, _fp_[, _skipkeys_[, _ensure_ascii_[, _check_circular_[, _allow_nan_[, _cls_[, _indent_[, _separators_[, _encoding_[, _default_[, _**kw_]]]]]]]]]])¶

Serialize obj as a JSON formatted stream to fp (a .write()-supporting file-like object).

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 aTypeError.

If ensure_ascii is False (default: True), then some chunks written to fp may be unicode instances, subject to normal Pythonstr to unicode coercion rules. Unless fp.write()explicitly understands unicode (as in codecs.getwriter()) this is likely to cause an error.

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 aValueError to serialize out of range float values (nan,inf, -inf) in strict compliance of the JSON specification, instead of using the JavaScript equivalents (NaN, Infinity, -Infinity).

If indent is a non-negative integer, then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0 will only insert newlines. None (the default) selects the most compact representation.

If separators is an (item_separator, dict_separator) tuple, then it will be used instead of the default (', ', ': ') separators. (',', ':') is the most compact JSON representation.

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 thedefault() method to serialize additional types), specify it with the_cls_ kwarg.

json.dumps(_obj_[, _skipkeys_[, _ensure_ascii_[, _check_circular_[, _allow_nan_[, _cls_[, _indent_[, _separators_[, _encoding_[, _default_[, _**kw_]]]]]]]]]])¶

Serialize obj to a JSON formatted str.

If ensure_ascii is False, then the return value will be aunicode instance. The other arguments have the same meaning as indump().

json.load(_fp_[, _encoding_[, _cls_[, _object_hook_[, _parse_float_[, _parse_int_[, _parse_constant_[, _object_pairs_hook_[, _**kw_]]]]]]]])¶

Deserialize fp (a .read()-supporting file-like object containing a JSON document) to a Python object.

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(encoding)(fp), or simply decoded to a unicode object and passed to loads().

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 thedict. 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 2.7: 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', 'null', 'true','false'. This can be used to raise an exception if invalid JSON numbers are encountered.

To use a custom JSONDecoder subclass, specify it with the clskwarg. Additional keyword arguments will be passed to the constructor of the class.

json.loads(_s_[, _encoding_[, _cls_[, _object_hook_[, _parse_float_[, _parse_int_[, _parse_constant_[, _object_pairs_hook_[, _**kw_]]]]]]]])¶

Deserialize s (a str or unicode instance containing a JSON document) to a Python object.

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.

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

18.2.2. Encoders and decoders¶

class json.JSONDecoder([_encoding_[, _object_hook_[, _parse_float_[, _parse_int_[, _parse_constant_[, _strict_[, _object_pairs_hook_]]]]]]])¶

Simple JSON decoder.

Performs the following translations in decoding by default:

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 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, if specified, will be called with the result of every JSON object decoded and its return value will be used in place of the givendict. 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 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 2.7: 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', 'null', 'true','false'. This can be used to raise an exception if invalid JSON numbers are encountered.

decode(s)¶

Return the Python representation of s (a str orunicode instance containing a JSON document)

raw_decode(s)¶

Decode a JSON document from s (a str or unicodebeginning 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.

class json.JSONEncoder([_skipkeys_[, _ensure_ascii_[, _check_circular_[, _allow_nan_[, _sort_keys_[, _indent_[, _separators_[, _encoding_[, _default_]]]]]]]]])¶

Extensible JSON encoder for Python data structures.

Supports the following objects and types by default:

To extend this to recognize other objects, subclass and implement adefault() 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), then it is a TypeError to attempt encoding of keys that are not str, int, long, float or None. If_skipkeys_ is True, such items are simply skipped.

If ensure_ascii is True (the default), the output is guaranteed to bestr 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.

If sort_keys is True (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 indent is a non-negative integer (it is None by default), then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0 will only insert newlines. None is the most compact representation.

If specified, separators should be an (item_separator, key_separator)tuple. The default is (', ', ': '). To get the most compact JSON representation, you should specify (',', ':') to eliminate whitespace.

If specified, default is 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.

default(o)¶

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

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)

encode(o)¶

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

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)