index.rst

:mod:`simplejson` --- JSON encoder and decoder

.. module:: simplejson
   :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:`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 2.5 and (currently) has significant performance advantages, even without using the optional C extension for speedups.

Development of simplejson happens on Github: http://github.com/simplejson/simplejson

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

Using Decimal instead of float:

>>> import simplejson as json
>>> from decimal import Decimal
>>> json.loads('1.1', use_decimal=True) == Decimal('1.1')
True
>>> json.dumps(Decimal('1.1'), use_decimal=True) == '1.1'
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]'

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 enclosed in double quotes: line 1 column 2 (char 2)

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[, use_decimal[, namedtuple_as_object[, tuple_as_array[, bigint_as_string[, sort_keys[, item_sort_key[, **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 string, then JSON array elements and object members
   will be pretty-printed with a newline followed by that string repeated
   for each level of nesting. ``None`` (the default) selects the most compact
   representation without any newlines. For backwards compatibility with
   versions of simplejson earlier than 2.1.0, an integer is also accepted
   and is converted to a string with that many spaces.

   .. versionchanged:: 2.1.0
      Changed *indent* from an integer number of spaces to a string.

   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'``.

   *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.

   If *use_decimal* is true (default: ``True``) then :class:`decimal.Decimal`
   will be natively serialized to JSON with full precision.

   .. versionchanged:: 2.1.0
      *use_decimal* is new in 2.1.0.

   .. versionchanged:: 2.2.0
      The default of *use_decimal* changed to ``True`` in 2.2.0.

   If *namedtuple_as_object* is true (default: ``True``),
   objects with ``_asdict()`` methods will be encoded
   as JSON objects.

   .. versionchanged:: 2.2.0
     *namedtuple_as_object* is new in 2.2.0.

   .. versionchanged:: 2.3.0
     *namedtuple_as_object* no longer requires that these objects be
     subclasses of :class:`tuple`.

   If *tuple_as_array* is true (default: ``True``),
   :class:`tuple` (and subclasses) will be encoded as JSON arrays.

   .. versionchanged:: 2.2.0
     *tuple_as_array* is new in 2.2.0.

   If *bigint_as_string* is true (default: ``False``), :class:`int`` ``2**53``
   and higher or lower than ``-2**53`` will be encoded as strings. This is to
   avoid the rounding that happens in Javascript otherwise. Note that this
   option loses type information, so use with extreme caution.

   .. versionchanged:: 2.4.0
     *bigint_as_string* is new in 2.4.0.

   If *sort_keys* is true (not 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 *item_sort_key* is a callable (not the default), then the output of
   dictionaries will be sorted with it. The callable will be used like this:
   ``sorted(dct.items(), key=item_sort_key)``. This option takes precedence
   over *sort_keys*.

   .. versionchanged:: 2.5.0
      *item_sort_key* is new in 2.5.0.

    .. 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[, use_decimal[, namedtuple_as_object[, tuple_as_array[, bigint_as_string[, sort_keys[, item_sort_key[, **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[, object_pairs_hook[, use_decimal[, **kw]]]]]]]]])

   Deserialize *fp* (a ``.read()``-supporting file-like object containing a JSON
   document) to a Python object. :exc:`JSONDecodeError` will be
   raised if the given JSON document is not valid.

   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.

   If *fp.read()* returns :class:`str` then decoded JSON strings that contain
   only ASCII characters may be parsed as :class:`str` for performance and
   memory reasons. If your code expects only :class:`unicode` the appropriate
   solution is to wrap fp with a reader as demonstrated above.

   *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,
   :class:`collections.OrderedDict` will remember the order of insertion). If
   *object_hook* is also defined, the *object_pairs_hook* takes priority.

   .. versionchanged:: 2.1.0
      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'``.  This can be used to
   raise an exception if invalid JSON numbers are encountered.

   If *use_decimal* is true (default: ``False``) then *parse_float* is set to
   :class:`decimal.Decimal`. This is a convenience for parity with the
   :func:`dump` parameter.

   .. versionchanged:: 2.1.0
      *use_decimal* is new in 2.1.0.

   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[, object_pairs_hook[, use_decimal[, **kw]]]]]]]]])

   Deserialize *s* (a :class:`str` or :class:`unicode` instance containing a JSON
   document) to a Python object. :exc:`JSONDecodeError` will be
   raised if the given JSON document is not valid.

   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.

   If *s* is a :class:`str` then decoded JSON strings that contain
   only ASCII characters may be parsed as :class:`str` for performance and
   memory reasons. If your code expects only :class:`unicode` the appropriate
   solution is decode *s* to :class:`unicode` prior to calling loads.

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

Encoders and decoders

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 is an optional function that 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 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, :class:`collections.OrderedDict` will remember the order of insertion). If object_hook is also defined, the object_pairs_hook takes priority.

.. versionchanged:: 2.1.0
   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'. 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)

   If *s* is a :class:`str` then decoded JSON strings that contain
   only ASCII characters may be parsed as :class:`str` for performance and
   memory reasons. If your code expects only :class:`unicode` the
   appropriate solution is decode *s* to :class:`unicode` prior to calling
   decode.

   :exc:`JSONDecodeError` will be raised if the given JSON
   document is not valid.

.. method:: raw_decode(s[, idx=0])

   Decode a JSON document from *s* (a :class:`str` or :class:`unicode`
   beginning with a JSON document) starting from the index *idx* 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, or to decode a string that has a series of
   JSON objects.

   :exc:`JSONDecodeError` will be raised if the given JSON
   document is not valid.

Extensible JSON encoder for Python data structures.

Supports the following objects and types by default:

Python	JSON
dict, namedtuple	object
list, tuple	array
str, unicode	string
int, long, float	number
True	true
False	false
None	null

.. versionchanged:: 2.2.0
   Changed *namedtuple* encoding from JSON array to object.

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 (not 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 item_sort_key is a callable (not the default), then the output of dictionaries will be sorted with it. The callable will be used like this: sorted(dct.items(), key=item_sort_key). This option takes precedence over sort_keys.

.. versionchanged:: 2.5.0
   *item_sort_key* is new in 2.5.0.

If indent is a string, then JSON array elements and object members will be pretty-printed with a newline followed by that string repeated for each level of nesting. None (the default) selects the most compact representation without any newlines. For backwards compatibility with versions of simplejson earlier than 2.1.0, an integer is also accepted and is converted to a string with that many spaces.

.. versionchanged:: 2.1.0
   Changed *indent* from an integer number of spaces to a string.

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'.

If namedtuple_as_object is true (default: True), objects with _asdict() methods will be encoded as JSON objects.

.. versionchanged:: 2.2.0
  *namedtuple_as_object* is new in 2.2.0.

.. versionchanged:: 2.3.0
  *namedtuple_as_object* no longer requires that these objects be
  subclasses of :class:`tuple`.

If tuple_as_array is true (default: True), :class:`tuple` (and subclasses) will be encoded as JSON arrays.

.. versionchanged:: 2.2.0
  *tuple_as_array* is new in 2.2.0.

If bigint_as_string is true (default: False), :class:`int`` 2**53 and higher or lower than -2**53 will be encoded as strings. This is to avoid the rounding that happens in Javascript otherwise. Note that this option loses type information, so use with extreme caution.

.. versionchanged:: 2.4.0
  *bigint_as_string* is new in 2.4.0.

.. 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`.

Subclass of :class:`JSONEncoder` that escapes &, <, and > for embedding in HTML.

.. versionchanged:: 2.1.0
   New in 2.1.0

Exceptions

.. exception:: JSONDecodeError(msg, doc, pos[, end])

    Subclass of :exc:`ValueError` with the following additional attributes:

    .. attribute:: msg

        The unformatted error message

    .. attribute:: doc

        The JSON document being parsed

    .. attribute:: pos

        The start index of doc where parsing failed

    .. attribute:: end

        The end index of doc where parsing failed (may be ``None``)

    .. attribute:: lineno

        The line corresponding to pos

    .. attribute:: colno

        The column corresponding to pos

    .. attribute:: endlineno

        The line corresponding to end (may be ``None``)

    .. attribute:: endcolno

        The column corresponding to end (may be ``None``)