:mod:`simplejson` --- JSON encoder and decoder ============================================== .. module:: simplejson :synopsis: Encode and decode the JSON format. .. moduleauthor:: Bob Ippolito .. sectionauthor:: Bob Ippolito JSON (JavaScript Object Notation) is a subset of JavaScript syntax (ECMA-262 3rd edition) used as a lightweight data interchange format. :mod:`simplejson` exposes an API familiar to users of the standard library :mod:`marshal` and :mod:`pickle` modules. It is the externally maintained version of the :mod:`json` library contained in Python 2.6, but maintains compatibility with Python 2.4 and Python 2.5 and (currently) has significant performance advantages, even without using the optional C extension for speedups. 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 StringIO import StringIO >>> io = StringIO() >>> json.dump(['streaming API'], io) >>> io.getvalue() '["streaming API"]' Compact encoding:: >>> import simplejson as json >>> json.dumps([1,2,3,{'4': 5, '6': 7}], separators=(',',':')) '[1,2,3,{"4":5,"6":7}]' Pretty printing:: >>> import simplejson as json >>> s = json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4) >>> print '\n'.join([l.rstrip() for l in s.splitlines()]) { "4": 5, "6": 7 } Decoding JSON:: >>> import simplejson as json >>> obj = [u'foo', {u'bar': [u'baz', None, 1.0, 2]}] >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]') == obj True >>> json.loads('"\\"foo\\bar"') == u'"foo\x08ar' True >>> from StringIO import StringIO >>> io = StringIO('["streaming API"]') >>> json.load(io)[0] == 'streaming API' 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(o) + " 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]' .. highlight:: none Using :mod:`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: 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:`long`, :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. It's best to leave the default settings, because they are safe and it is highly optimized. 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. If *allow_nan* is true, their JavaScript equivalents will be used (``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 specified, *separators* should be an ``(item_separator, dict_separator)`` tuple. By default, ``(', ', ': ')`` are used. To get the most compact JSON representation, you should specify ``(',', ':')`` to eliminate whitespace. *encoding* is the character encoding for str instances, default is ``'utf-8'``. 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 :exc:`TypeError`. If not specified, :exc:`TypeError` is always raised in those cases. 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. .. note:: JSON is not a framed protocol so unlike :mod:`pickle` or :mod:`marshal` it does not make sense to serialize more than one JSON document without some container protocol to delimit them. .. 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`. Note that the default *ensure_ascii* setting has much better performance. .. function:: load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, **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`. The default setting of ``'utf-8'`` is fastest and should be using whenever possible. *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). *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'``. 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. .. note:: :func:`load` will read the rest of the file-like object as a string and then call :func:`loads`. 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 use :func:`loads`. .. function:: loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, **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:`load`. Encoders and decoders --------------------- .. class:: JSONDecoder([encoding[, object_hook[, parse_float[, parse_int[, parse_constant[, strict]]]]]]) Simple JSON decoder. Performs the following translations in decoding by default: +---------------+-------------------+ | JSON | Python | +===============+===================+ | object | dict | +---------------+-------------------+ | array | list | +---------------+-------------------+ | string | unicode | +---------------+-------------------+ | number (int) | int, long | +---------------+-------------------+ | 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). *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'``. This can be used to raise an exception if invalid JSON numbers are encountered. *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, if ``False`` then control characters will be allowed in strings. .. 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, long, 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, 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 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 false (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. By default, ``(', ', ': ')`` are used. 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 :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:: >>> import simplejson as json >>> json.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) Note that :meth:`encode` has much better performance than :meth:`iterencode`.