1 :mod:`json` --- JSON encoder and decoder
2 ========================================
5 :synopsis: Encode and decode the JSON format.
6 .. moduleauthor:: Bob Ippolito <bob@redivi.com>
7 .. sectionauthor:: Bob Ippolito <bob@redivi.com>
10 JSON (JavaScript Object Notation) <http://json.org> is a subset of JavaScript
11 syntax (ECMA-262 3rd edition) used as a lightweight data interchange format.
13 :mod:`json` exposes an API familiar to users of the standard library
14 :mod:`marshal` and :mod:`pickle` modules.
16 Encoding basic Python object hierarchies::
19 >>> json.dumps(['foo', {'bar': ('baz', None, 1.0, 2)}])
20 '["foo", {"bar": ["baz", null, 1.0, 2]}]'
21 >>> print json.dumps("\"foo\bar")
23 >>> print json.dumps(u'\u1234')
25 >>> print json.dumps('\\')
27 >>> print json.dumps({"c": 0, "b": 0, "a": 0}, sort_keys=True)
28 {"a": 0, "b": 0, "c": 0}
29 >>> from StringIO import StringIO
31 >>> json.dump(['streaming API'], io)
38 >>> json.dumps([1,2,3,{'4': 5, '6': 7}], separators=(',',':'))
39 '[1,2,3,{"4":5,"6":7}]'
44 >>> print json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4)
53 >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]')
54 [u'foo', {u'bar': [u'baz', None, 1.0, 2]}]
55 >>> json.loads('"\\"foo\\bar"')
57 >>> from StringIO import StringIO
58 >>> io = StringIO('["streaming API"]')
62 Specializing JSON object decoding::
65 >>> def as_complex(dct):
66 ... if '__complex__' in dct:
67 ... return complex(dct['real'], dct['imag'])
70 >>> json.loads('{"__complex__": true, "real": 1, "imag": 2}',
71 ... object_hook=as_complex)
74 >>> json.loads('1.1', parse_float=decimal.Decimal)
77 Extending :class:`JSONEncoder`::
80 >>> class ComplexEncoder(json.JSONEncoder):
81 ... def default(self, obj):
82 ... if isinstance(obj, complex):
83 ... return [obj.real, obj.imag]
84 ... return json.JSONEncoder.default(self, obj)
86 >>> dumps(2 + 1j, cls=ComplexEncoder)
88 >>> ComplexEncoder().encode(2 + 1j)
90 >>> list(ComplexEncoder().iterencode(2 + 1j))
91 ['[', '2.0', ', ', '1.0', ']']
96 Using json.tool from the shell to validate and pretty-print::
98 $ echo '{"json":"obj"}' | python -mjson.tool
102 $ echo '{ 1.2:3.4}' | python -mjson.tool
103 Expecting property name: line 1 column 2 (char 2)
105 .. highlight:: python
109 The JSON produced by this module's default settings is a subset of
110 YAML, so it may be used as a serializer for that as well.
116 .. function:: dump(obj, fp[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, **kw]]]]]]]]]])
118 Serialize *obj* as a JSON formatted stream to *fp* (a ``.write()``-supporting
121 If *skipkeys* is ``True`` (default: ``False``), then dict keys that are not
122 of a basic type (:class:`str`, :class:`unicode`, :class:`int`, :class:`long`,
123 :class:`float`, :class:`bool`, ``None``) will be skipped instead of raising a
126 If *ensure_ascii* is ``False`` (default: ``True``), then some chunks written
127 to *fp* may be :class:`unicode` instances, subject to normal Python
128 :class:`str` to :class:`unicode` coercion rules. Unless ``fp.write()``
129 explicitly understands :class:`unicode` (as in :func:`codecs.getwriter`) this
130 is likely to cause an error.
132 If *check_circular* is ``False`` (default: ``True``), then the circular
133 reference check for container types will be skipped and a circular reference
134 will result in an :exc:`OverflowError` (or worse).
136 If *allow_nan* is ``False`` (default: ``True``), then it will be a
137 :exc:`ValueError` to serialize out of range :class:`float` values (``nan``,
138 ``inf``, ``-inf``) in strict compliance of the JSON specification, instead of
139 using the JavaScript equivalents (``NaN``, ``Infinity``, ``-Infinity``).
141 If *indent* is a non-negative integer, then JSON array elements and object
142 members will be pretty-printed with that indent level. An indent level of 0
143 will only insert newlines. ``None`` (the default) selects the most compact
146 If *separators* is an ``(item_separator, dict_separator)`` tuple, then it
147 will be used instead of the default ``(', ', ': ')`` separators. ``(',',
148 ':')`` is the most compact JSON representation.
150 *encoding* is the character encoding for str instances, default is UTF-8.
152 *default(obj)* is a function that should return a serializable version of
153 *obj* or raise :exc:`TypeError`. The default simply raises :exc:`TypeError`.
155 To use a custom :class:`JSONEncoder`` subclass (e.g. one that overrides the
156 :meth:`default` method to serialize additional types), specify it with the
160 .. function:: dumps(obj[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, **kw]]]]]]]]]])
162 Serialize *obj* to a JSON formatted :class:`str`.
164 If *ensure_ascii* is ``False``, then the return value will be a
165 :class:`unicode` instance. The other arguments have the same meaning as in
169 .. function load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, **kw]]]]]]])
171 Deserialize *fp* (a ``.read()``-supporting file-like object containing a JSON
172 document) to a Python object.
174 If the contents of *fp* are encoded with an ASCII based encoding other than
175 UTF-8 (e.g. latin-1), then an appropriate *encoding* name must be specified.
176 Encodings that are not ASCII based (such as UCS-2) are not allowed, and
177 should be wrapped with ``codecs.getreader(fp)(encoding)``, or simply decoded
178 to a :class:`unicode` object and passed to :func:`loads`.
180 *object_hook* is an optional function that will be called with the result of
181 any object literal decode (a :class:`dict`). The return value of
182 *object_hook* will be used instead of the :class:`dict`. This feature can be used
183 to implement custom decoders (e.g. JSON-RPC class hinting).
185 *parse_float*, if specified, will be called with the string of every JSON
186 float to be decoded. By default, this is equivalent to ``float(num_str)``.
187 This can be used to use another datatype or parser for JSON floats
188 (e.g. :class:`decimal.Decimal`).
190 *parse_int*, if specified, will be called with the string of every JSON int
191 to be decoded. By default, this is equivalent to ``int(num_str)``. This can
192 be used to use another datatype or parser for JSON integers
193 (e.g. :class:`float`).
195 *parse_constant*, if specified, will be called with one of the following
196 strings: ``'-Infinity'``, ``'Infinity'``, ``'NaN'``, ``'null'``, ``'true'``,
197 ``'false'``. This can be used to raise an exception if invalid JSON numbers
200 To use a custom :class:`JSONDecoder` subclass, specify it with the ``cls``
201 kwarg. Additional keyword arguments will be passed to the constructor of the
205 .. function loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, **kw]]]]]]])
207 Deserialize *s* (a :class:`str` or :class:`unicode` instance containing a JSON
208 document) to a Python object.
210 If *s* is a :class:`str` instance and is encoded with an ASCII based encoding
211 other than UTF-8 (e.g. latin-1), then an appropriate *encoding* name must be
212 specified. Encodings that are not ASCII based (such as UCS-2) are not
213 allowed and should be decoded to :class:`unicode` first.
215 The other arguments have the same meaning as in :func:`dump`.
218 Encoders and decoders
219 ---------------------
221 .. class:: JSONDecoder([encoding[, object_hook[, parse_float[, parse_int[, parse_constant[, strict]]]]]])
225 Performs the following translations in decoding by default:
227 +---------------+-------------------+
229 +===============+===================+
231 +---------------+-------------------+
233 +---------------+-------------------+
235 +---------------+-------------------+
236 | number (int) | int, long |
237 +---------------+-------------------+
238 | number (real) | float |
239 +---------------+-------------------+
241 +---------------+-------------------+
243 +---------------+-------------------+
245 +---------------+-------------------+
247 It also understands ``NaN``, ``Infinity``, and ``-Infinity`` as their
248 corresponding ``float`` values, which is outside the JSON spec.
250 *encoding* determines the encoding used to interpret any :class:`str` objects
251 decoded by this instance (UTF-8 by default). It has no effect when decoding
252 :class:`unicode` objects.
254 Note that currently only encodings that are a superset of ASCII work, strings
255 of other encodings should be passed in as :class:`unicode`.
257 *object_hook*, if specified, will be called with the result of every JSON
258 object decoded and its return value will be used in place of the given
259 :class:`dict`. This can be used to provide custom deserializations (e.g. to
260 support JSON-RPC class hinting).
262 *parse_float*, if specified, will be called with the string of every JSON
263 float to be decoded. By default, this is equivalent to ``float(num_str)``.
264 This can be used to use another datatype or parser for JSON floats
265 (e.g. :class:`decimal.Decimal`).
267 *parse_int*, if specified, will be called with the string of every JSON int
268 to be decoded. By default, this is equivalent to ``int(num_str)``. This can
269 be used to use another datatype or parser for JSON integers
270 (e.g. :class:`float`).
272 *parse_constant*, if specified, will be called with one of the following
273 strings: ``'-Infinity'``, ``'Infinity'``, ``'NaN'``, ``'null'``, ``'true'``,
274 ``'false'``. This can be used to raise an exception if invalid JSON numbers
278 .. method:: decode(s)
280 Return the Python representation of *s* (a :class:`str` or
281 :class:`unicode` instance containing a JSON document)
283 .. method:: raw_decode(s)
285 Decode a JSON document from *s* (a :class:`str` or :class:`unicode`
286 beginning with a JSON document) and return a 2-tuple of the Python
287 representation and the index in *s* where the document ended.
289 This can be used to decode a JSON document from a string that may have
290 extraneous data at the end.
293 .. class:: JSONEncoder([skipkeys[, ensure_ascii[, check_circular[, allow_nan[, sort_keys[, indent[, separators[, encoding[, default]]]]]]]]])
295 Extensible JSON encoder for Python data structures.
297 Supports the following objects and types by default:
299 +-------------------+---------------+
301 +===================+===============+
303 +-------------------+---------------+
304 | list, tuple | array |
305 +-------------------+---------------+
306 | str, unicode | string |
307 +-------------------+---------------+
308 | int, long, float | number |
309 +-------------------+---------------+
311 +-------------------+---------------+
313 +-------------------+---------------+
315 +-------------------+---------------+
317 To extend this to recognize other objects, subclass and implement a
318 :meth:`default` method with another method that returns a serializable object
319 for ``o`` if possible, otherwise it should call the superclass implementation
320 (to raise :exc:`TypeError`).
322 If *skipkeys* is ``False`` (the default), then it is a :exc:`TypeError` to
323 attempt encoding of keys that are not str, int, long, float or None. If
324 *skipkeys* is ``True``, such items are simply skipped.
326 If *ensure_ascii* is ``True`` (the default), the output is guaranteed to be
327 :class:`str` objects with all incoming unicode characters escaped. If
328 *ensure_ascii* is ``False``, the output will be a unicode object.
330 If *check_circular* is ``True`` (the default), then lists, dicts, and custom
331 encoded objects will be checked for circular references during encoding to
332 prevent an infinite recursion (which would cause an :exc:`OverflowError`).
333 Otherwise, no such check takes place.
335 If *allow_nan* is ``True`` (the default), then ``NaN``, ``Infinity``, and
336 ``-Infinity`` will be encoded as such. This behavior is not JSON
337 specification compliant, but is consistent with most JavaScript based
338 encoders and decoders. Otherwise, it will be a :exc:`ValueError` to encode
341 If *sort_keys* is ``True`` (the default), then the output of dictionaries
342 will be sorted by key; this is useful for regression tests to ensure that
343 JSON serializations can be compared on a day-to-day basis.
345 If *indent* is a non-negative integer (it is ``None`` by default), then JSON
346 array elements and object members will be pretty-printed with that indent
347 level. An indent level of 0 will only insert newlines. ``None`` is the most
348 compact representation.
350 If specified, *separators* should be an ``(item_separator, key_separator)``
351 tuple. The default is ``(', ', ': ')``. To get the most compact JSON
352 representation, you should specify ``(',', ':')`` to eliminate whitespace.
354 If specified, *default* is a function that gets called for objects that can't
355 otherwise be serialized. It should return a JSON encodable version of the
356 object or raise a :exc:`TypeError`.
358 If *encoding* is not ``None``, then all input strings will be transformed
359 into unicode using that encoding prior to JSON-encoding. The default is
363 .. method:: default(o)
365 Implement this method in a subclass such that it returns a serializable
366 object for *o*, or calls the base implementation (to raise a
369 For example, to support arbitrary iterators, you could implement default
372 def default(self, o):
378 return list(iterable)
379 return JSONEncoder.default(self, o)
382 .. method:: encode(o)
384 Return a JSON string representation of a Python data structure, *o*. For
387 >>> JSONEncoder().encode({"foo": ["bar", "baz"]})
388 '{"foo": ["bar", "baz"]}'
391 .. method:: iterencode(o)
393 Encode the given object, *o*, and yield each string representation as
394 available. For example::
396 for chunk in JSONEncoder().iterencode(bigobject):
397 mysocket.write(chunk)