path: root/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>`_, specified by
:rfc:`7159` (which obsoletes :rfc:`4627`) and by
`ECMA-404 <http://www.ecma-international.org/publications/standards/Ecma-404.htm>`_,
is a lightweight data interchange format inspired by
`JavaScript <http://en.wikipedia.org/wiki/JavaScript>`_ object literal syntax
(although it is not a strict subset of JavaScript [#rfc-errata]_ ).

:mod:`simplejson` is a simple, fast, complete, correct and extensible
JSON encoder and decoder for Python. It is pure Python code
with no dependencies, but includes an optional C extension
for a serious speed boost.

: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, but maintains
compatibility with the latest Python 3.8+ releases back to Python 3.3
as well as the legacy Python 2.5 - Python 2.7 releases.

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 simplejson.compat import StringIO
    >>> io = StringIO()
    >>> json.dump(['streaming API'], io)
    >>> io.getvalue()
    '["streaming API"]'

Compact encoding::

    >>> import simplejson as json
    >>> obj = [1,2,3,{'4': 5, '6': 7}]
    >>> json.dumps(obj, separators=(',', ':'), sort_keys=True)
    '[1,2,3,{"4":5,"6":7}]'

Pretty printing::

    >>> import simplejson as json
    >>> print(json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4 * ' '))
    {
        "4": 5,
        "6": 7
    }

Decoding JSON::

    >>> import simplejson as json
    >>> obj = ['foo', {'bar': ['baz', None, 1.0, 2]}]
    >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]') == obj
    True
    >>> json.loads('"\\"foo\\bar"') == '"foo\x08ar'
    True
    >>> from simplejson.compat 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(obj) + " 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:: bash

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 3 (char 2)

.. highlight:: python

Parsing multiple documents serialized as JSON lines (newline-delimited JSON)::

    >>> import simplejson as json
    >>> def loads_lines(docs):
    ...     for doc in docs.splitlines():
    ...         yield json.loads(doc)
    ...
    >>> sum(doc["count"] for doc in loads_lines('{"count":1}\n{"count":2}\n{"count":3}\n'))
    6

Serializing multiple objects to JSON lines (newline-delimited JSON)::

    >>> import simplejson as json
    >>> def dumps_lines(objs):
    ...     for obj in objs:
    ...         yield json.dumps(obj, separators=(',',':')) + '\n'
    ...
    >>> ''.join(dumps_lines([{'count': 1}, {'count': 2}, {'count': 3}]))
    '{"count":1}\n{"count":2}\n{"count":3}\n'

.. note::

   JSON is a subset of `YAML <http://yaml.org/>`_ 1.2. The JSON produced by
   this module's default settings (in particular, the default *separators*
   value) is also a subset of YAML 1.0 and 1.1. This module can thus also be
   used as a YAML serializer.


Basic Usage
-----------

.. function:: dump(obj, fp, skipkeys=False, ensure_ascii=True, \
                   check_circular=True, allow_nan=False, cls=None, \
                   indent=None, separators=None, encoding='utf-8', \
                   default=None, use_decimal=True, \
                   namedtuple_as_object=True, tuple_as_array=True, \
                   bigint_as_string=False, sort_keys=False, \
                   item_sort_key=None, for_json=None, ignore_nan=False, \
                   int_as_string_bitcount=None, iterable_as_array=False, **kw)

    Serialize *obj* as a JSON formatted stream to *fp*
    (a ``.write()``-supporting file-like object) using this
    :ref:`conversion table <py-to-json-table>`.

    The :mod:`simplejson` module will produce :class:`str` objects in
    Python 3, not :class:`bytes` objects. Therefore, ``fp.write()`` must
    support :class:`str` input.

    See :func:`dumps` for a description of each argument. The only difference
    is that this function writes the resulting JSON document to *fp* instead
    of returning it.

    .. note::

        When using Python 2, if *ensure_ascii* is set to false,
        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.

.. function:: dumps(obj, skipkeys=False, ensure_ascii=True, \
                    check_circular=True, allow_nan=False, cls=None, \
                    indent=None, separators=None, encoding='utf-8', \
                    default=None, use_decimal=True, \
                    namedtuple_as_object=True, tuple_as_array=True, \
                    bigint_as_string=False, sort_keys=False, \
                    item_sort_key=None, for_json=None, ignore_nan=False, \
                    int_as_string_bitcount=None, iterable_as_array=False, **kw)

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

    If *skipkeys* is true (default: ``False``), then dict keys that are not
    of a basic type (:class:`str`, :class:`int`, :class:`long`,
    :class:`float`, :class:`bool`, ``None``) will be skipped instead of
    raising a :exc:`TypeError`.

    .. note::

        When using Python 2, both :class:`str` and :class:`unicode` are
        considered to be basic types that represent text.

    If *ensure_ascii* is false (default: ``True``), then the output may
    contain non-ASCII characters, so long as they do not need to be escaped
    by JSON. When it is true, all non-ASCII characters are escaped.

    .. note::

        When using Python 2, if *ensure_ascii* is set to false,
        the result may be a :class:`unicode` object. By default, as a memory
        optimization, the result would be a :class:`str` object.

    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: ``False``), then it will be a
    :exc:`ValueError` to serialize out of range :class:`float` values
    (``nan``, ``inf``, ``-inf``) in strict compliance of the original
    JSON specification. If *allow_nan* is true, their JavaScript equivalents
    will be used (``NaN``, ``Infinity``, ``-Infinity``). See also *ignore_nan*
    for ECMA-262 compliant behavior.

    .. versionchanged:: 3.19.0
        The default for *allow_nan* was changed to False for better spec
        compliance.

    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.

    If specified, *separators* should be an
    ``(item_separator, key_separator)`` tuple.  The default is
    ``(', ', ': ')`` if *indent* is ``None`` and ``(',', ': ')``
    otherwise.  To get the most compact JSON representation,
    you should specify ``(',', ':')`` to eliminate whitespace.

    If *encoding* is not ``None``, then all input :class:`bytes` objects in
    Python 3 and 8-bit strings in Python 2 will be transformed
    into unicode using that encoding prior to JSON-encoding.  The default is
    ``'utf-8'``.  If *encoding* is ``None``, then all :class:`bytes` objects
    will be passed to the *default* function in Python 3

    .. versionchanged:: 3.15.0
        ``encoding=None`` disables serializing :class:`bytes` by default in
        Python 3.

    *default(obj)* is a function that should return a serializable version of
    *obj* or raise :exc:`TypeError`. The default implementation always 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.

    .. note::

        Subclassing is not recommended. Use the *default* kwarg
        or *for_json* instead. This is faster and more portable.

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

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

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

    If *iterable_as_array* is true (default: ``False``),
    any object not in the above table that implements ``__iter__()``
    will be encoded as a JSON array.

    .. versionchanged:: 3.8.0
        *iterable_as_array* is new in 3.8.0.

    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.
    See also *int_as_string_bitcount*.

    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*.

    If *for_json* is true (not the default), objects with a ``for_json()``
    method will use the return value of that method for encoding as JSON
    instead of the object.

    If *ignore_nan* is true (default: ``False``), then out of range
    :class:`float` values (``nan``, ``inf``, ``-inf``) will be serialized as
    ``null`` in compliance with the ECMA-262 specification. If true, this will
    override *allow_nan*.

    If *int_as_string_bitcount* is a positive number ``n`` (default: ``None``),
    :class:`int` ``2**n`` and higher or lower than ``-2**n`` 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.
    See also *bigint_as_string* (which is equivalent to `int_as_string_bitcount=53`).

    .. 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:: load(fp, encoding='utf-8', cls=None, object_hook=None, \
                   parse_float=None, parse_int=None, \
                   parse_constant=None, object_pairs_hook=None, \
                   use_decimal=None, allow_nan=False, **kw)

   Deserialize *fp* (a ``.read()``-supporting file-like object containing a JSON
   document) to a Python object using this
   :ref:`conversion table <json-to-py-table>`. :exc:`JSONDecodeError` will be
   raised if the given JSON document is not valid.

   If *fp.read()* returns :class:`bytes`, such as a file opened in binary mode,
   then an appropriate *encoding* should be specified (the default is UTF-8).

    .. 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`.

    .. note::

        In Python 2, :class:`str` is considered to be :class:`bytes` and this
        is the default behavior of all :class:`file` objects. 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
        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.

   See :func:`loads` for a description of each argument. The only difference
   is that this function reads the JSON document from a file-like object *fp*
   instead of a :class:`str` or :class:`bytes`.

.. function:: loads(s, encoding='utf-8', cls=None, object_hook=None, \
                    parse_float=None, parse_int=None, \
                    parse_constant=None, object_pairs_hook=None, \
                    use_decimal=None, allow_nan=False, **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.

    .. note::

        In Python 2, :class:`str` is considered to be :class:`bytes` as above,
        if your JSON is using an encoding that is not ASCII based, then you must
        decode to :class:`unicode` first.

        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. Additionally,
        decoded JSON strings that contain only ASCII characters may be parsed as
        :class:`str` instead of :class:`unicode` for performance and memory
        reasons. If your code expects only :class:`unicode` the appropriate
        solution is decode *s* to :class:`unicode` prior to calling :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 <http://www.jsonrpc.org>`_
    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.

    *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`).

    .. versionchanged:: 3.19.0
        The integer to string conversion length limitation introduced in
        Python 3.11 has been backported. An attempt to parse an integer
        with more than 4300 digits will result in an exception unless a
        suitable alternative parser is specified
        (e.g. :class:`decimal.Decimal`)

    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.

    If *iterable_as_array* is true (default: ``False``),
    any object not in the above table that implements ``__iter__()``
    will be encoded as a JSON array.

    .. versionchanged:: 3.8.0
        *iterable_as_array* is new in 3.8.0.

    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. You probably shouldn't do this.

    .. note::

        Subclassing is not recommended. You should use *object_hook* or
        *object_pairs_hook*. This is faster and more portable than subclassing.


    *allow_nan*, if True (default false), will allow the parser to
    accept the non-standard floats
    ``NaN``, ``Infinity``, and ``-Infinity``.

    .. versionchanged:: 3.19.0

        This argument was added to make it possible to use the legacy behavior
        now that the parser is more strict about compliance to the standard.

    *parse_constant*, if specified, will be
    called with one of the following strings: ``'-Infinity'``,
    ``'Infinity'``, ``'NaN'``. It is not recommended to use this feature,
    as it is rare to parse non-compliant JSON containing these values.


Encoders and decoders
---------------------

.. class:: JSONDecoder(encoding='utf-8', object_hook=None, parse_float=None, \
                       parse_int=None, parse_constant=None, \
                       object_pairs_hook=None, strict=True, allow_nan=False)

   Simple JSON decoder.

   Performs the following translations in decoding by default:

   .. _json-to-py-table:

   +---------------+-----------+-----------+
   | JSON          | Python 2  | Python 3  |
   +===============+===========+===========+
   | object        | dict      | dict      |
   +---------------+-----------+-----------+
   | array         | list      | list      |
   +---------------+-----------+-----------+
   | string        | unicode   | str       |
   +---------------+-----------+-----------+
   | number (int)  | int, long | int       |
   +---------------+-----------+-----------+
   | number (real) | float     | float     |
   +---------------+-----------+-----------+
   | true          | True      | True      |
   +---------------+-----------+-----------+
   | false         | False     | False     |
   +---------------+-----------+-----------+
   | null          | None      | None      |
   +---------------+-----------+-----------+

   When *allow_nan* is True, 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.

   *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`).

    .. versionchanged:: 3.19.0
        The integer to string conversion length limitation introduced in
        Python 3.11 has been backported. An attempt to parse an integer
        with more than 4300 digits will result in an exception unless a
        suitable alternative parser is specified
        (e.g. :class:`decimal.Decimal`)

    *parse_constant*, if specified, will be
    called with one of the following strings: ``'-Infinity'``,
    ``'Infinity'``, ``'NaN'``. It is not recommended to use this feature,
    as it is rare to parse non-compliant JSON containing these values.

   *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.

   *allow_nan* when True (not the default), the decoder will allow
   ``NaN``, ``Infinity``, and ``-Infinity`` as their corresponding floats.

    .. versionchanged:: 3.19.0
        This argument was added to make it behave closer to the spec by
        default. The previous behavior can be restored by setting this to
        False.

   .. method:: decode(s)

      Return the Python representation of the JSON document *s*. See
      :func:`loads` for details. It is preferable to use that rather
      than this class.

   .. 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.

.. class:: JSONEncoder(skipkeys=False, ensure_ascii=True, \
                       check_circular=True, allow_nan=False, sort_keys=False, \
                       indent=None, separators=None, encoding='utf-8', \
                       default=None, use_decimal=True, \
                       namedtuple_as_object=True, tuple_as_array=True, \
                       bigint_as_string=False, item_sort_key=None, \
                       for_json=True, ignore_nan=False, \
                       int_as_string_bitcount=None, iterable_as_array=False)

   Extensible JSON encoder for Python data structures.

   Supports the following objects and types by default:

   .. _py-to-json-table:

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

   .. note:: The JSON format only permits strings to be used as object
      keys, thus any Python dicts to be encoded should only have string keys.
      For backwards compatibility, several other types are automatically
      coerced to strings: int, long, float, Decimal, bool, and None.
      It is error-prone to rely on this behavior, so avoid it when possible.
      Dictionaries with other types used as keys should be pre-processed or
      wrapped in another type with an appropriate `for_json` method to
      transform the keys during encoding.

   When *allow_nan* is True, it also understands
   ``NaN``, ``Infinity``, and ``-Infinity`` as their
   corresponding ``float`` values, which is outside the JSON spec.

   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`).

    .. note::

        Subclassing is not recommended. You should use the *default*
        or *for_json* kwarg. This is faster and more portable than subclassing.

   If *skipkeys* is false (the default), then it is a :exc:`TypeError` to
   attempt encoding of keys that are not str, int, long, float, Decimal, bool,
   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 (not the default), then ``NaN``, ``Infinity``, and
   ``-Infinity`` will be encoded as such. This behavior is not JSON
   specification compliant. Otherwise, it will be a :exc:`ValueError` to encode
   such floats. See also *ignore_nan* for ECMA-262 compliant behavior.

    .. versionchanged:: 3.19.0
        This default is now False to make it behave closer to the spec.
        The previous behavior can be restored by setting this to
        False.

   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*.

   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.

   If specified, *separators* should be an ``(item_separator, key_separator)``
   tuple.  The default is ``(', ', ': ')`` if *indent* is ``None`` and
   ``(',', ': ')`` otherwise.  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 :class:`bytes` objects in
   Python 3 and 8-bit strings in Python 2 will be transformed
   into unicode using that encoding prior to JSON-encoding.  The default is
   ``'utf-8'``.  If *encoding* is ``None``, then all :class:`bytes` objects
   will be passed to the :meth:`default` method in Python 3

   .. versionchanged:: 3.15.0
      ``encoding=None`` disables serializing :class:`bytes` by default in
      Python 3.

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

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

   If *iterable_as_array* is true (default: ``False``),
   any object not in the above table that implements ``__iter__()``
   will be encoded as a JSON array.

   .. versionchanged:: 3.8.0
     *iterable_as_array* is new in 3.8.0.

   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.

   If *for_json* is true (default: ``False``), objects with a ``for_json()``
   method will use the return value of that method for encoding as JSON instead
   of the object.

   If *ignore_nan* is true (default: ``False``), then out of range
   :class:`float` values (``nan``, ``inf``, ``-inf``) will be serialized as
   ``null`` in compliance with the ECMA-262 specification. If true, this will
   override *allow_nan*.

   .. 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)

    .. note::

        Subclassing is not recommended. You should implement this
        as a function and pass it to the *default* kwarg of :func:`dumps`.
        This is faster and more portable than subclassing. The
        semantics are the same, but without the self argument or the
        call to the super implementation.

   .. 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`.

.. class:: JSONEncoderForHTML(skipkeys=False, ensure_ascii=True, \
                              check_circular=True, allow_nan=False, \
                              sort_keys=False, indent=None, separators=None, \
                              encoding='utf-8', \
                              default=None, use_decimal=True, \
                              namedtuple_as_object=True, \
                              tuple_as_array=True, \
                              bigint_as_string=False, item_sort_key=None, \
                              for_json=True, ignore_nan=False, \
                              int_as_string_bitcount=None)

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

   It also escapes the characters U+2028 (LINE SEPARATOR) and
   U+2029 (PARAGRAPH SEPARATOR), irrespective of the *ensure_ascii* setting,
   as these characters are not valid in JavaScript strings (see
   http://timelessrepo.com/json-isnt-a-javascript-subset).

Exceptions
----------

.. exception:: JSONDecodeError(msg, doc, pos, end=None)

    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``)


Standard Compliance and Interoperability
----------------------------------------

The JSON format is specified by :rfc:`7159` and by
`ECMA-404 <http://www.ecma-international.org/publications/standards/Ecma-404.htm>`_.
This section details this module's level of compliance with the RFC.
For simplicity, :class:`JSONEncoder` and :class:`JSONDecoder` subclasses, and
parameters other than those explicitly mentioned, are not considered.

This module does not comply with the RFC in a strict fashion, implementing some
extensions that are valid JavaScript but not valid JSON.  In particular:

- Infinite and NaN number values are accepted and output;
- Repeated names within an object are accepted, and only the value of the last
  name-value pair is used.

Since the RFC permits RFC-compliant parsers to accept input texts that are not
RFC-compliant, this module's deserializer is technically RFC-compliant under
default settings.


Character Encodings
^^^^^^^^^^^^^^^^^^^

The RFC recommends that JSON be represented using either UTF-8, UTF-16, or
UTF-32, with UTF-8 being the recommended default for maximum interoperability.

As permitted, though not required, by the RFC, this module's serializer sets
*ensure_ascii=True* by default, thus escaping the output so that the resulting
strings only contain ASCII characters.

Other than the *ensure_ascii* parameter, this module is defined strictly in
terms of conversion between Python objects and
:class:`Unicode strings <str>`, and thus does not otherwise directly address
the issue of character encodings.

The RFC prohibits adding a byte order mark (BOM) to the start of a JSON text,
and this module's serializer does not add a BOM to its output.
The RFC permits, but does not require, JSON deserializers to ignore an initial
BOM in their input.  This module's deserializer will ignore an initial BOM, if
present.

The RFC does not explicitly forbid JSON strings which contain byte sequences
that don't correspond to valid Unicode characters (e.g. unpaired UTF-16
surrogates), but it does note that they may cause interoperability problems.
By default, this module accepts and outputs (when present in the original
:class:`str`) codepoints for such sequences.

Infinite and NaN Number Values
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The RFC does not permit the representation of infinite or NaN number values.
Despite that, by default, this module accepts and outputs ``Infinity``,
``-Infinity``, and ``NaN`` as if they were valid JSON number literal values
if the allow_nan flag is enabled::

   >>> # Neither of these calls raises an exception, but the results are not valid JSON
   >>> json.dumps(float('-inf'), allow_nan=True)
   '-Infinity'
   >>> json.dumps(float('nan'), allow_nan=True)
   'NaN'
   >>> # Same when deserializing
   >>> json.loads('-Infinity', allow_nan=True)
   -inf
   >>> json.loads('NaN', allow_nan=True)
   nan
   >>> # ignore_nan uses the ECMA-262 behavior to serialize these as null
   >>> json.dumps(float('-inf'), ignore_nan=True)
   'null'
   >>> json.dumps(float('nan'), ignore_nan=True)
   'null'

In the serializer, the *allow_nan* parameter can be used to alter this
behavior. In the deserializer, the *allow_nan* and
*parse_constant* parameters can be used to alter this behavior.


Repeated Names Within an Object
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The RFC specifies that the names within a JSON object should be unique, but
does not mandate how repeated names in JSON objects should be handled.  By
default, this module does not raise an exception; instead, it ignores all but
the last name-value pair for a given name::

   >>> weird_json = '{"x": 1, "x": 2, "x": 3}'
   >>> json.loads(weird_json) == {'x': 3}
   True

The *object_pairs_hook* parameter can be used to alter this behavior.


Top-level Non-Object, Non-Array Values
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The old version of JSON specified by the obsolete :rfc:`4627` required that
the top-level value of a JSON text must be either a JSON object or array
(Python :class:`dict` or :class:`list`), and could not be a JSON null,
boolean, number, or string value.  :rfc:`7159` removed that restriction, and
this module does not and has never implemented that restriction in either its
serializer or its deserializer.

Regardless, for maximum interoperability, you may wish to voluntarily adhere
to the restriction yourself.


Implementation Limitations
^^^^^^^^^^^^^^^^^^^^^^^^^^

Some JSON deserializer implementations may set limits on:

* the size of accepted JSON texts
* the maximum level of nesting of JSON objects and arrays
* the range and precision of JSON numbers
* the content and maximum length of JSON strings

This module does not impose any such limits beyond those of the relevant
Python datatypes themselves or the Python interpreter itself.

When serializing to JSON, beware any such limitations in applications that may
consume your JSON.  In particular, it is common for JSON numbers to be
deserialized into IEEE 754 double precision numbers and thus subject to that
representation's range and precision limitations.  This is especially relevant
when serializing Python :class:`int` values of extremely large magnitude, or
when serializing instances of "exotic" numerical types such as
:class:`decimal.Decimal`.

.. highlight:: bash

.. _json-commandline:

Command Line Interface
----------------------

The :mod:`simplejson.tool` module provides a simple command line interface to
validate and pretty-print JSON.

If the optional :option:`infile` and :option:`outfile` arguments are not
specified, :attr:`sys.stdin` and :attr:`sys.stdout` will be used respectively::

    $ 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 1)


Command line options
^^^^^^^^^^^^^^^^^^^^

.. cmdoption:: infile

   The JSON file to be validated or pretty-printed::

      $ python -m simplejson.tool mp_films.json
      [
          {
              "title": "And Now for Something Completely Different",
              "year": 1971
          },
          {
              "title": "Monty Python and the Holy Grail",
              "year": 1975
          }
      ]

   If *infile* is not specified, read from :attr:`sys.stdin`.

.. cmdoption:: outfile

   Write the output of the *infile* to the given *outfile*. Otherwise, write it
   to :attr:`sys.stdout`.

.. rubric:: Footnotes

.. [#rfc-errata] As noted in `the errata for RFC 7159
   <http://www.rfc-editor.org/errata_search.php?rfc=7159>`_,
   JSON permits literal U+2028 (LINE SEPARATOR) and
   U+2029 (PARAGRAPH SEPARATOR) characters in strings, whereas JavaScript
   (as of ECMAScript Edition 5.1) does not.