1 :mod:`json` --- JSON encoder and decoder

     2 ========================================

     3 

     4 .. module:: json

     5    :synopsis: Encode and decode the JSON format.

     6 .. moduleauthor:: Bob Ippolito <bob@redivi.com>

     7 .. sectionauthor:: Bob Ippolito <bob@redivi.com>

     8 .. versionadded:: 2.6

     9 

    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.

    12 

    13 :mod:`json` exposes an API familiar to users of the standard library

    14 :mod:`marshal` and :mod:`pickle` modules.

    15 

    16 Encoding basic Python object hierarchies::

    17     

    18     >>> import json

    19     >>> json.dumps(['foo', {'bar': ('baz', None, 1.0, 2)}])

    20     '["foo", {"bar": ["baz", null, 1.0, 2]}]'

    21     >>> print json.dumps("\"foo\bar")

    22     "\"foo\bar"

    23     >>> print json.dumps(u'\u1234')

    24     "\u1234"

    25     >>> print json.dumps('\\')

    26     "\\"

    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

    30     >>> io = StringIO()

    31     >>> json.dump(['streaming API'], io)

    32     >>> io.getvalue()

    33     '["streaming API"]'

    34 

    35 Compact encoding::

    36 

    37     >>> import json

    38     >>> json.dumps([1,2,3,{'4': 5, '6': 7}], separators=(',',':'))

    39     '[1,2,3,{"4":5,"6":7}]'

    40 

    41 Pretty printing::

    42 

    43     >>> import json

    44     >>> print json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4)

    45     {

    46         "4": 5, 

    47         "6": 7

    48     }

    49 

    50 Decoding JSON::

    51     

    52     >>> import json

    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"')

    56     u'"foo\x08ar'

    57     >>> from StringIO import StringIO

    58     >>> io = StringIO('["streaming API"]')

    59     >>> json.load(io)

    60     [u'streaming API']

    61 

    62 Specializing JSON object decoding::

    63 

    64     >>> import json

    65     >>> def as_complex(dct):

    66     ...     if '__complex__' in dct:

    67     ...         return complex(dct['real'], dct['imag'])

    68     ...     return dct

    69     ... 

    70     >>> json.loads('{"__complex__": true, "real": 1, "imag": 2}',

    71     ...     object_hook=as_complex)

    72     (1+2j)

    73     >>> import decimal

    74     >>> json.loads('1.1', parse_float=decimal.Decimal)

    75     Decimal('1.1')

    76 

    77 Extending :class:`JSONEncoder`::

    78     

    79     >>> import json

    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)

    85     ... 

    86     >>> dumps(2 + 1j, cls=ComplexEncoder)

    87     '[2.0, 1.0]'

    88     >>> ComplexEncoder().encode(2 + 1j)

    89     '[2.0, 1.0]'

    90     >>> list(ComplexEncoder().iterencode(2 + 1j))

    91     ['[', '2.0', ', ', '1.0', ']']

    92     

    93 

    94 .. highlight:: none

    95 

    96 Using json.tool from the shell to validate and pretty-print::

    97     

    98     $ echo '{"json":"obj"}' | python -mjson.tool

    99     {

   100         "json": "obj"

   101     }

   102     $ echo '{ 1.2:3.4}' | python -mjson.tool

   103     Expecting property name: line 1 column 2 (char 2)

   104 

   105 .. highlight:: python

   106 

   107 .. note:: 

   108 

   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.

   111 

   112 

   113 Basic Usage

   114 -----------

   115 

   116 .. function:: dump(obj, fp[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, **kw]]]]]]]]]])

   117 

   118    Serialize *obj* as a JSON formatted stream to *fp* (a ``.write()``-supporting

   119    file-like object).

   120 

   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

   124    :exc:`TypeError`.

   125 

   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.

   131 

   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).

   135 

   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``).

   140 

   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

   144    representation.

   145 

   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.

   149 

   150    *encoding* is the character encoding for str instances, default is UTF-8.

   151 

   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`.

   154 

   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

   157    *cls* kwarg.

   158 

   159 

   160 .. function:: dumps(obj[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, **kw]]]]]]]]]])

   161 

   162    Serialize *obj* to a JSON formatted :class:`str`.

   163 

   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

   166    :func:`dump`.

   167 

   168 

   169 .. function load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, **kw]]]]]]])

   170 

   171    Deserialize *fp* (a ``.read()``-supporting file-like object containing a JSON

   172    document) to a Python object.

   173 

   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`.

   179 

   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).

   184 

   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`).

   189 

   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`).

   194 

   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

   198    are encountered.

   199 

   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

   202    class.

   203 

   204 

   205 .. function loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, **kw]]]]]]])

   206 

   207    Deserialize *s* (a :class:`str` or :class:`unicode` instance containing a JSON

   208    document) to a Python object.

   209 

   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.

   214 

   215    The other arguments have the same meaning as in :func:`dump`.

   216 

   217 

   218 Encoders and decoders

   219 ---------------------

   220 

   221 .. class:: JSONDecoder([encoding[, object_hook[, parse_float[, parse_int[, parse_constant[, strict]]]]]])

   222 

   223    Simple JSON decoder.

   224 

   225    Performs the following translations in decoding by default:

   226 

   227    +---------------+-------------------+

   228    | JSON          | Python            |

   229    +===============+===================+

   230    | object        | dict              |

   231    +---------------+-------------------+

   232    | array         | list              |

   233    +---------------+-------------------+

   234    | string        | unicode           |

   235    +---------------+-------------------+

   236    | number (int)  | int, long         |

   237    +---------------+-------------------+

   238    | number (real) | float             |

   239    +---------------+-------------------+

   240    | true          | True              |

   241    +---------------+-------------------+

   242    | false         | False             |

   243    +---------------+-------------------+

   244    | null          | None              |

   245    +---------------+-------------------+

   246 

   247    It also understands ``NaN``, ``Infinity``, and ``-Infinity`` as their

   248    corresponding ``float`` values, which is outside the JSON spec.

   249 

   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.

   253 

   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`.

   256 

   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).

   261 

   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`).

   266 

   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`).

   271 

   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

   275    are encountered.

   276 

   277 

   278    .. method:: decode(s)

   279 

   280       Return the Python representation of *s* (a :class:`str` or

   281       :class:`unicode` instance containing a JSON document)

   282 

   283    .. method:: raw_decode(s)

   284 

   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.

   288 

   289       This can be used to decode a JSON document from a string that may have

   290       extraneous data at the end.

   291 

   292 

   293 .. class:: JSONEncoder([skipkeys[, ensure_ascii[, check_circular[, allow_nan[, sort_keys[, indent[, separators[, encoding[, default]]]]]]]]])

   294 

   295    Extensible JSON encoder for Python data structures.

   296 

   297    Supports the following objects and types by default:

   298 

   299    +-------------------+---------------+

   300    | Python            | JSON          |

   301    +===================+===============+

   302    | dict              | object        |

   303    +-------------------+---------------+

   304    | list, tuple       | array         |

   305    +-------------------+---------------+

   306    | str, unicode      | string        |

   307    +-------------------+---------------+

   308    | int, long, float  | number        |

   309    +-------------------+---------------+

   310    | True              | true          |

   311    +-------------------+---------------+

   312    | False             | false         |

   313    +-------------------+---------------+

   314    | None              | null          |

   315    +-------------------+---------------+

   316 

   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`).

   321 

   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.

   325 

   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.

   329 

   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.

   334 

   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

   339    such floats.

   340 

   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.

   344 

   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.

   349 

   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.

   353 

   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`.

   357 

   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

   360    UTF-8.

   361 

   362 

   363    .. method:: default(o)

   364 

   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

   367       :exc:`TypeError`).

   368 

   369       For example, to support arbitrary iterators, you could implement default

   370       like this::

   371             

   372          def default(self, o):

   373             try:

   374                 iterable = iter(o)

   375             except TypeError:

   376                 pass

   377             else:

   378                 return list(iterable)

   379             return JSONEncoder.default(self, o)

   380 

   381 

   382    .. method:: encode(o)

   383 

   384       Return a JSON string representation of a Python data structure, *o*.  For

   385       example::

   386 

   387         >>> JSONEncoder().encode({"foo": ["bar", "baz"]})

   388         '{"foo": ["bar", "baz"]}'

   389 

   390 

   391    .. method:: iterencode(o)

   392 

   393       Encode the given object, *o*, and yield each string representation as

   394       available.  For example::

   395             

   396             for chunk in JSONEncoder().iterencode(bigobject):

   397                 mysocket.write(chunk)