| :mod:`json` --- JSON encoder and decoder |
| ======================================== |
| |
| .. module:: json |
| :synopsis: Encode and decode the JSON format. |
| .. moduleauthor:: Bob Ippolito <bob@redivi.com> |
| .. sectionauthor:: Bob Ippolito <bob@redivi.com> |
| |
| JSON (JavaScript Object Notation) <http://json.org> is a subset of JavaScript |
| syntax (ECMA-262 3rd edition) used as a lightweight data interchange format. |
| |
| :mod:`json` exposes an API familiar to users of the standard library |
| :mod:`marshal` and :mod:`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 :class:`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', ']'] |
| |
| |
| .. highlight:: none |
| |
| 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) |
| |
| .. highlight:: python |
| |
| .. 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. |
| |
| |
| Basic Usage |
| ----------- |
| |
| .. function:: 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 (:class:`str`, :class:`unicode`, :class:`int`, |
| :class:`float`, :class:`bool`, ``None``) will be skipped instead of raising a |
| :exc:`TypeError`. |
| |
| If *ensure_ascii* is ``False`` (default: ``True``), then some chunks written |
| to *fp* may be :class:`unicode` instances, subject to normal Python |
| :class:`str` to :class:`unicode` coercion rules. Unless ``fp.write()`` |
| explicitly understands :class:`unicode` (as in :func:`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 :exc:`OverflowError` (or worse). |
| |
| If *allow_nan* is ``False`` (default: ``True``), then it will be a |
| :exc:`ValueError` to serialize out of range :class:`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 :exc:`TypeError`. The default simply raises :exc:`TypeError`. |
| |
| To use a custom :class:`JSONEncoder` subclass (e.g. one that overrides the |
| :meth:`default` method to serialize additional types), specify it with the |
| *cls* kwarg. |
| |
| |
| .. function:: dumps(obj[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, **kw]]]]]]]]]]) |
| |
| Serialize *obj* to a JSON formatted :class:`str`. |
| |
| If *ensure_ascii* is ``False``, then the return value will be a |
| :class:`unicode` instance. The other arguments have the same meaning as in |
| :func:`dump`. |
| |
| |
| .. function:: 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(fp)(encoding)``, or simply decoded |
| to a :class:`unicode` object and passed to :func:`loads`. |
| |
| *object_hook* is an optional function that will be called with the result of |
| any object literal decode (a :class:`dict`). The return value of |
| *object_hook* will be used instead of the :class:`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 |
| :class:`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, |
| :func:`collections.OrderedDict` will remember the order of insertion). If |
| *object_hook* is also defined, the *object_pairs_hook* takes priority. |
| |
| .. versionchanged:: 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. :class:`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. :class:`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 :class:`JSONDecoder` subclass, specify it with the ``cls`` |
| kwarg. Additional keyword arguments will be passed to the constructor of the |
| class. |
| |
| |
| .. function:: loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]]) |
| |
| Deserialize *s* (a :class:`str` or :class:`unicode` instance containing a JSON |
| document) to a Python object. |
| |
| If *s* is a :class:`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 :class:`unicode` first. |
| |
| The other arguments have the same meaning as in :func:`dump`. |
| |
| |
| Encoders and decoders |
| --------------------- |
| |
| .. class:: 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: |
| |
| +---------------+-------------------+ |
| | JSON | Python | |
| +===============+===================+ |
| | object | dict | |
| +---------------+-------------------+ |
| | array | list | |
| +---------------+-------------------+ |
| | string | unicode | |
| +---------------+-------------------+ |
| | 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. |
| |
| *encoding* determines the encoding used to interpret any :class:`str` objects |
| decoded by this instance (UTF-8 by default). It has no effect when decoding |
| :class:`unicode` objects. |
| |
| Note that currently only encodings that are a superset of ASCII work, strings |
| of other encodings should be passed in as :class:`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 given |
| :class:`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 :class:`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, |
| :func:`collections.OrderedDict` will remember the order of insertion). If |
| *object_hook* is also defined, the *object_pairs_hook* takes priority. |
| |
| .. versionchanged:: 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. :class:`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. :class:`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. |
| |
| |
| .. method:: decode(s) |
| |
| Return the Python representation of *s* (a :class:`str` or |
| :class:`unicode` instance containing a JSON document) |
| |
| .. method:: raw_decode(s) |
| |
| Decode a JSON document from *s* (a :class:`str` or :class:`unicode` |
| 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. |
| |
| |
| .. class:: 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: |
| |
| +-------------------+---------------+ |
| | Python | JSON | |
| +===================+===============+ |
| | dict | object | |
| +-------------------+---------------+ |
| | list, tuple | array | |
| +-------------------+---------------+ |
| | str, unicode | string | |
| +-------------------+---------------+ |
| | int, float | number | |
| +-------------------+---------------+ |
| | True | true | |
| +-------------------+---------------+ |
| | False | false | |
| +-------------------+---------------+ |
| | None | null | |
| +-------------------+---------------+ |
| |
| To extend this to recognize other objects, subclass and implement a |
| :meth:`default` method with another method that returns a serializable object |
| for ``o`` if possible, otherwise it should call the superclass implementation |
| (to raise :exc:`TypeError`). |
| |
| If *skipkeys* is ``False`` (the default), then it is a :exc:`TypeError` to |
| attempt encoding of 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 be |
| :class:`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 :exc:`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 :exc:`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 :exc:`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. |
| |
| |
| .. method:: 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 |
| :exc:`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) |
| |
| |
| .. method:: encode(o) |
| |
| Return a JSON string representation of a Python data structure, *o*. For |
| example:: |
| |
| >>> JSONEncoder().encode({"foo": ["bar", "baz"]}) |
| '{"foo": ["bar", "baz"]}' |
| |
| |
| .. method:: 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) |