/Doc/library/json.rst
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- :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>
- .. versionadded:: 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.
- :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(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 :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:`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.
- 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[, **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 :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).
- *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[, **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]]]]]])
- 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'``, ``'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, 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 ``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)