: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(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).

   *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)