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:mod:`json` --- JSON encoder and decoder
========================================
.. module:: json
:synopsis: Encode and decode the JSON format.
.. moduleauthor:: Bob Ippolito <bob@redivi.com>
.. sectionauthor:: Bob Ippolito <bob@redivi.com>
**Source code:** :source:`Lib/json/__init__.py`
--------------
`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 <https://en.wikipedia.org/wiki/JavaScript>`_ object literal syntax
(although it is not a strict subset of JavaScript [#rfc-errata]_ ).
:mod:`json` exposes an API familiar to users of the standard library
:mod:`marshal` and :mod:`pickle` modules.
Encoding basic Python object hierarchies::
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>>> 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('\u1234'))
"\u1234"
>>> print(json.dumps('\\'))
"\\"
>>> print(json.dumps({"c": 0, "b": 0, "a": 0}, sort_keys=True))
{"a": 0, "b": 0, "c": 0}
>>> from io 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))
{
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"4": 5,
"6": 7
}
Decoding JSON::
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>>> import json
>>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]')
['foo', {'bar': ['baz', None, 1.0, 2]}]
>>> json.loads('"\\"foo\\bar"')
'"foo\x08ar'
>>> from io import StringIO
>>> io = StringIO('["streaming API"]')
>>> json.load(io)
['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`::
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>>> import json
>>> class ComplexEncoder(json.JSONEncoder):
... def default(self, obj):
... if isinstance(obj, complex):
... return [obj.real, obj.imag]
... # Let the base class default method raise the TypeError
... return json.JSONEncoder.default(self, obj)
...
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>>> json.dumps(2 + 1j, cls=ComplexEncoder)
'[2.0, 1.0]'
>>> ComplexEncoder().encode(2 + 1j)
'[2.0, 1.0]'
>>> list(ComplexEncoder().iterencode(2 + 1j))
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['[2.0', ', 1.0', ']']
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Using :mod:`json.tool` from the shell to validate and pretty-print:
.. code-block:: shell-session
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$ echo '{"json":"obj"}' | python -m json.tool
{
"json": "obj"
}
$ echo '{1.2:3.4}' | python -m json.tool
Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
See :ref:`json-commandline` for detailed documentation.
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.. 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.
.. note::
This module's encoders and decoders preserve input and output order by
default. Order is only lost if the underlying containers are unordered.
Prior to Python 3.7, :class:`dict` was not guaranteed to be ordered, so
inputs and outputs were typically scrambled unless
:class:`collections.OrderedDict` was specifically requested. Starting
with Python 3.7, the regular :class:`dict` became order preserving, so
it is no longer necessary to specify :class:`collections.OrderedDict` for
JSON generation and parsing.
Basic Usage
-----------
.. function:: dump(obj, fp, *, skipkeys=False, ensure_ascii=True, \
check_circular=True, allow_nan=True, cls=None, \
indent=None, separators=None, default=None, \
sort_keys=False, **kw)
Serialize *obj* as a JSON formatted stream to *fp* (a ``.write()``-supporting
:term:`file-like object`) using this :ref:`conversion table
<py-to-json-table>`.
If *skipkeys* is true (default: ``False``), then dict keys that are not
of a basic type (:class:`str`, :class:`int`, :class:`float`, :class:`bool`,
``None``) will be skipped instead of raising a :exc:`TypeError`.
The :mod:`json` module always produces :class:`str` objects, not
:class:`bytes` objects. Therefore, ``fp.write()`` must support :class:`str`
input.
If *ensure_ascii* is true (the default), the output is guaranteed to
have all incoming non-ASCII characters escaped. If *ensure_ascii* is
false, these characters will be output as-is.
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 (``NaN``,
``Infinity``, ``-Infinity``) will be used.
If *indent* is a non-negative integer or string, then JSON array elements and
object members will be pretty-printed with that indent level. An indent level
of 0, negative, or ``""`` will only insert newlines. ``None`` (the default)
selects the most compact representation. Using a positive integer indent
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indents that many spaces per level. If *indent* is a string (such as ``"\t"``),
that string is used to indent each level.
.. versionchanged:: 3.2
Allow strings for *indent* in addition to integers.
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.
.. versionchanged:: 3.4
Use ``(',', ': ')`` as default if *indent* is not ``None``.
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 not specified, :exc:`TypeError`
is raised.
If *sort_keys* is true (default: ``False``), then the output of
dictionaries will be sorted by key.
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; otherwise :class:`JSONEncoder` is used.
.. versionchanged:: 3.6
All optional parameters are now :ref:`keyword-only <keyword-only_parameter>`.
.. note::
Unlike :mod:`pickle` and :mod:`marshal`, JSON is not a framed protocol,
so trying to serialize multiple objects with repeated calls to
:func:`dump` using the same *fp* will result in an invalid JSON file.
.. function:: dumps(obj, *, skipkeys=False, ensure_ascii=True, \
check_circular=True, allow_nan=True, cls=None, \
indent=None, separators=None, default=None, \
sort_keys=False, **kw)
Serialize *obj* to a JSON formatted :class:`str` using this :ref:`conversion
table <py-to-json-table>`. The arguments have the same meaning as in
:func:`dump`.
.. note::
Keys in key/value pairs of JSON are always of the type :class:`str`. When
a dictionary is converted into JSON, all the keys of the dictionary are
coerced to strings. As a result of this, if a dictionary is converted
into JSON and then back into a dictionary, the dictionary may not equal
the original one. That is, ``loads(dumps(x)) != x`` if x has non-string
keys.
.. function:: load(fp, *, cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, **kw)
Deserialize *fp* (a ``.read()``-supporting :term:`text file` or
:term:`binary file` containing a JSON document) to a Python object using
this :ref:`conversion table <json-to-py-table>`.
*object_hook* is an optional function that will be called with the result of
Merged revisions 70768,71657,71721,71729,71794,71976,72036-72037,72079,72085,72131-72134,72191,72197-72198,72219,72221,72225,72303,72434,72467,72476 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r70768 | andrew.kuchling | 2009-03-30 17:29:15 -0500 (Mon, 30 Mar 2009) | 1 line Typo fixes ........ r71657 | vinay.sajip | 2009-04-16 14:07:37 -0500 (Thu, 16 Apr 2009) | 1 line Issue #5768: Change to Unicode output logic and test case for same. ........ r71721 | benjamin.peterson | 2009-04-18 14:26:19 -0500 (Sat, 18 Apr 2009) | 1 line fix a few nits in unittest.py #5771 ........ r71729 | benjamin.peterson | 2009-04-18 16:03:10 -0500 (Sat, 18 Apr 2009) | 1 line move test to a more appropiate one ........ r71794 | vinay.sajip | 2009-04-22 07:10:47 -0500 (Wed, 22 Apr 2009) | 2 lines Issue #5170: Fixed regression caused when fixing #5768. ........ r71976 | mark.dickinson | 2009-04-26 14:54:55 -0500 (Sun, 26 Apr 2009) | 2 lines Fix typo in function name ........ r72036 | georg.brandl | 2009-04-27 12:04:23 -0500 (Mon, 27 Apr 2009) | 1 line #5848: small unittest doc patch. ........ r72037 | georg.brandl | 2009-04-27 12:09:53 -0500 (Mon, 27 Apr 2009) | 1 line #5840: dont claim we dont support TLS. ........ r72079 | r.david.murray | 2009-04-28 14:02:55 -0500 (Tue, 28 Apr 2009) | 2 lines Remove spurious 'u'. ........ r72085 | georg.brandl | 2009-04-28 16:48:35 -0500 (Tue, 28 Apr 2009) | 1 line Make the doctests in the docs pass, except for those in the turtle module. ........ r72131 | benjamin.peterson | 2009-04-29 17:43:35 -0500 (Wed, 29 Apr 2009) | 1 line fix test_shutil on ZFS #5676 ........ r72132 | georg.brandl | 2009-04-29 17:44:07 -0500 (Wed, 29 Apr 2009) | 1 line #5878: fix repr of re object. ........ r72133 | benjamin.peterson | 2009-04-29 17:44:15 -0500 (Wed, 29 Apr 2009) | 1 line make sure mode is removable while cleaning up test droppings ........ r72134 | benjamin.peterson | 2009-04-29 19:06:33 -0500 (Wed, 29 Apr 2009) | 1 line make sure to close file ........ r72191 | michael.foord | 2009-05-02 06:43:06 -0500 (Sat, 02 May 2009) | 9 lines Adds an exit parameter to unittest.main(). If False main no longer calls sys.exit. Closes issue 3379. Michael Foord ........ r72197 | benjamin.peterson | 2009-05-02 11:24:37 -0500 (Sat, 02 May 2009) | 1 line don't let sys.argv be used in the tests ........ r72198 | andrew.kuchling | 2009-05-02 12:12:15 -0500 (Sat, 02 May 2009) | 1 line Add items ........ r72219 | michael.foord | 2009-05-02 15:15:05 -0500 (Sat, 02 May 2009) | 8 lines Add addCleanup and doCleanups to unittest.TestCase. Closes issue 5679. Michael Foord ........ r72221 | benjamin.peterson | 2009-05-02 15:26:53 -0500 (Sat, 02 May 2009) | 1 line add myself ........ r72225 | michael.foord | 2009-05-02 17:43:34 -0500 (Sat, 02 May 2009) | 1 line ........ r72303 | benjamin.peterson | 2009-05-04 19:55:24 -0500 (Mon, 04 May 2009) | 1 line using sys._getframe(x), where x > 0 doesnt' work on IronPython ........ r72434 | r.david.murray | 2009-05-07 13:09:58 -0500 (Thu, 07 May 2009) | 2 lines Pre-opened test file needs to be opened in binary mode. ........ r72467 | georg.brandl | 2009-05-08 07:17:34 -0500 (Fri, 08 May 2009) | 1 line Fix name. ........ r72476 | thomas.heller | 2009-05-08 15:09:40 -0500 (Fri, 08 May 2009) | 4 lines Add a file that contains diffs between offical libffi files and the files in this repository. Should make it easier to merge new libffi versions. ........
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any object literal decoded (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
Merged revisions 70768,71657,71721,71729,71794,71976,72036-72037,72079,72085,72131-72134,72191,72197-72198,72219,72221,72225,72303,72434,72467,72476 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r70768 | andrew.kuchling | 2009-03-30 17:29:15 -0500 (Mon, 30 Mar 2009) | 1 line Typo fixes ........ r71657 | vinay.sajip | 2009-04-16 14:07:37 -0500 (Thu, 16 Apr 2009) | 1 line Issue #5768: Change to Unicode output logic and test case for same. ........ r71721 | benjamin.peterson | 2009-04-18 14:26:19 -0500 (Sat, 18 Apr 2009) | 1 line fix a few nits in unittest.py #5771 ........ r71729 | benjamin.peterson | 2009-04-18 16:03:10 -0500 (Sat, 18 Apr 2009) | 1 line move test to a more appropiate one ........ r71794 | vinay.sajip | 2009-04-22 07:10:47 -0500 (Wed, 22 Apr 2009) | 2 lines Issue #5170: Fixed regression caused when fixing #5768. ........ r71976 | mark.dickinson | 2009-04-26 14:54:55 -0500 (Sun, 26 Apr 2009) | 2 lines Fix typo in function name ........ r72036 | georg.brandl | 2009-04-27 12:04:23 -0500 (Mon, 27 Apr 2009) | 1 line #5848: small unittest doc patch. ........ r72037 | georg.brandl | 2009-04-27 12:09:53 -0500 (Mon, 27 Apr 2009) | 1 line #5840: dont claim we dont support TLS. ........ r72079 | r.david.murray | 2009-04-28 14:02:55 -0500 (Tue, 28 Apr 2009) | 2 lines Remove spurious 'u'. ........ r72085 | georg.brandl | 2009-04-28 16:48:35 -0500 (Tue, 28 Apr 2009) | 1 line Make the doctests in the docs pass, except for those in the turtle module. ........ r72131 | benjamin.peterson | 2009-04-29 17:43:35 -0500 (Wed, 29 Apr 2009) | 1 line fix test_shutil on ZFS #5676 ........ r72132 | georg.brandl | 2009-04-29 17:44:07 -0500 (Wed, 29 Apr 2009) | 1 line #5878: fix repr of re object. ........ r72133 | benjamin.peterson | 2009-04-29 17:44:15 -0500 (Wed, 29 Apr 2009) | 1 line make sure mode is removable while cleaning up test droppings ........ r72134 | benjamin.peterson | 2009-04-29 19:06:33 -0500 (Wed, 29 Apr 2009) | 1 line make sure to close file ........ r72191 | michael.foord | 2009-05-02 06:43:06 -0500 (Sat, 02 May 2009) | 9 lines Adds an exit parameter to unittest.main(). If False main no longer calls sys.exit. Closes issue 3379. Michael Foord ........ r72197 | benjamin.peterson | 2009-05-02 11:24:37 -0500 (Sat, 02 May 2009) | 1 line don't let sys.argv be used in the tests ........ r72198 | andrew.kuchling | 2009-05-02 12:12:15 -0500 (Sat, 02 May 2009) | 1 line Add items ........ r72219 | michael.foord | 2009-05-02 15:15:05 -0500 (Sat, 02 May 2009) | 8 lines Add addCleanup and doCleanups to unittest.TestCase. Closes issue 5679. Michael Foord ........ r72221 | benjamin.peterson | 2009-05-02 15:26:53 -0500 (Sat, 02 May 2009) | 1 line add myself ........ r72225 | michael.foord | 2009-05-02 17:43:34 -0500 (Sat, 02 May 2009) | 1 line ........ r72303 | benjamin.peterson | 2009-05-04 19:55:24 -0500 (Mon, 04 May 2009) | 1 line using sys._getframe(x), where x > 0 doesnt' work on IronPython ........ r72434 | r.david.murray | 2009-05-07 13:09:58 -0500 (Thu, 07 May 2009) | 2 lines Pre-opened test file needs to be opened in binary mode. ........ r72467 | georg.brandl | 2009-05-08 07:17:34 -0500 (Fri, 08 May 2009) | 1 line Fix name. ........ r72476 | thomas.heller | 2009-05-08 15:09:40 -0500 (Fri, 08 May 2009) | 4 lines Add a file that contains diffs between offical libffi files and the files in this repository. Should make it easier to merge new libffi versions. ........
2009-05-08 17:42:26 -03:00
result of any object literal decoded 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.
If *object_hook* is also defined, the *object_pairs_hook* takes priority.
.. versionchanged:: 3.1
2009-04-26 00:34:06 -03:00
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.
.. versionchanged:: 3.1
*parse_constant* doesn't get called on 'null', 'true', 'false' anymore.
To use a custom :class:`JSONDecoder` subclass, specify it with the ``cls``
kwarg; otherwise :class:`JSONDecoder` is used. Additional keyword arguments
will be passed to the constructor of the class.
If the data being deserialized is not a valid JSON document, a
:exc:`JSONDecodeError` will be raised.
.. versionchanged:: 3.6
All optional parameters are now :ref:`keyword-only <keyword-only_parameter>`.
.. versionchanged:: 3.6
*fp* can now be a :term:`binary file`. The input encoding should be
UTF-8, UTF-16 or UTF-32.
.. function:: loads(s, *, cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, **kw)
Deserialize *s* (a :class:`str`, :class:`bytes` or :class:`bytearray`
instance containing a JSON document) to a Python object using this
:ref:`conversion table <json-to-py-table>`.
The other arguments have the same meaning as in :func:`load`.
If the data being deserialized is not a valid JSON document, a
:exc:`JSONDecodeError` will be raised.
.. versionchanged:: 3.6
*s* can now be of type :class:`bytes` or :class:`bytearray`. The
input encoding should be UTF-8, UTF-16 or UTF-32.
.. versionchanged:: 3.9
The keyword argument *encoding* has been removed.
Encoders and Decoders
---------------------
.. class:: JSONDecoder(*, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, strict=True, object_pairs_hook=None)
Simple JSON decoder.
Performs the following translations in decoding by default:
.. _json-to-py-table:
+---------------+-------------------+
| JSON | Python |
+===============+===================+
| object | dict |
+---------------+-------------------+
| array | list |
+---------------+-------------------+
| string | str |
+---------------+-------------------+
2009-04-11 15:18:16 -03:00
| number (int) | int |
+---------------+-------------------+
| 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.
*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).
*object_pairs_hook*, if specified will be called with the result of every
JSON object decoded 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. If *object_hook* is also
defined, the *object_pairs_hook* takes priority.
.. versionchanged:: 3.1
2009-04-26 00:34:06 -03:00
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 *strict* is false (``True`` is the default), then control characters
will be allowed inside strings. Control characters in this context are
those with character codes in the 0--31 range, including ``'\t'`` (tab),
``'\n'``, ``'\r'`` and ``'\0'``.
If the data being deserialized is not a valid JSON document, a
:exc:`JSONDecodeError` will be raised.
.. versionchanged:: 3.6
All parameters are now :ref:`keyword-only <keyword-only_parameter>`.
.. method:: decode(s)
Return the Python representation of *s* (a :class:`str` instance
containing a JSON document).
:exc:`JSONDecodeError` will be raised if the given JSON document is not
valid.
.. method:: raw_decode(s)
Decode a JSON document from *s* (a :class:`str` 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=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None)
Extensible JSON encoder for Python data structures.
Supports the following objects and types by default:
.. _py-to-json-table:
+----------------------------------------+---------------+
| Python | JSON |
+========================================+===============+
| dict | object |
+----------------------------------------+---------------+
| list, tuple | array |
+----------------------------------------+---------------+
| str | string |
+----------------------------------------+---------------+
| int, float, int- & float-derived Enums | number |
+----------------------------------------+---------------+
| True | true |
+----------------------------------------+---------------+
| False | false |
+----------------------------------------+---------------+
| None | null |
+----------------------------------------+---------------+
.. versionchanged:: 3.4
Added support for int- and float-derived Enum classes.
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 :class:`str`, :class:`int`,
:class:`float` or ``None``. If *skipkeys* is true, such items are simply
skipped.
If *ensure_ascii* is true (the default), the output is guaranteed to
have all incoming non-ASCII characters escaped. If *ensure_ascii* is
false, these characters will be output as-is.
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 (default: ``False``), 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 or string, then JSON array elements and
object members will be pretty-printed with that indent level. An indent level
of 0, negative, or ``""`` will only insert newlines. ``None`` (the default)
selects the most compact representation. Using a positive integer indent
indents that many spaces per level. If *indent* is a string (such as ``"\t"``),
that string is used to indent each level.
.. versionchanged:: 3.2
Allow strings for *indent* in addition to integers.
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.
.. versionchanged:: 3.4
Use ``(',', ': ')`` as default if *indent* is not ``None``.
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 not specified, :exc:`TypeError`
is raised.
.. versionchanged:: 3.6
All parameters are now :ref:`keyword-only <keyword-only_parameter>`.
.. 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::
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def default(self, o):
try:
Devil merge! Merged revisions 66561,66564,66580,66610,66614,66618,66624-66625,66628-66629,66643,66645,66660-66665 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r66561 | benjamin.peterson | 2008-09-22 17:13:29 -0500 (Mon, 22 Sep 2008) | 1 line clean up docs for platform's linux_distribution and dist functions ........ r66564 | benjamin.peterson | 2008-09-23 08:32:46 -0500 (Tue, 23 Sep 2008) | 1 line mention how to override boolean evaluation ........ r66580 | georg.brandl | 2008-09-24 04:47:55 -0500 (Wed, 24 Sep 2008) | 2 lines Indentation normalization. ........ r66610 | andrew.kuchling | 2008-09-24 12:27:55 -0500 (Wed, 24 Sep 2008) | 1 line Improve wording ........ r66614 | benjamin.peterson | 2008-09-24 17:11:59 -0500 (Wed, 24 Sep 2008) | 4 lines #3950 fix missing scale factors in turtle.py reviewers: Georg, Benjamin ........ r66618 | benjamin.peterson | 2008-09-25 15:35:45 -0500 (Thu, 25 Sep 2008) | 1 line add a NEWs entry for r66614 ........ r66624 | raymond.hettinger | 2008-09-25 18:31:52 -0500 (Thu, 25 Sep 2008) | 1 line Fix namedtuple bug reported by Glenn Linderman. Template did not form correctly if the field names were input in Unicode. ........ r66625 | benjamin.peterson | 2008-09-25 21:58:36 -0500 (Thu, 25 Sep 2008) | 1 line add the beginnings of a C-API 2 -> 3 porting guide ........ r66628 | benjamin.peterson | 2008-09-26 15:52:06 -0500 (Fri, 26 Sep 2008) | 1 line add an 'other options' section ........ r66629 | georg.brandl | 2008-09-26 16:15:21 -0500 (Fri, 26 Sep 2008) | 2 lines typos. ........ r66643 | andrew.kuchling | 2008-09-27 09:12:33 -0500 (Sat, 27 Sep 2008) | 1 line Add a last bunch of items ........ r66645 | benjamin.peterson | 2008-09-27 11:23:55 -0500 (Sat, 27 Sep 2008) | 1 line 2to3's api should be considered unstable ........ r66660 | andrew.kuchling | 2008-09-27 17:54:08 -0500 (Sat, 27 Sep 2008) | 1 line #3510: future-proof text ........ r66661 | benjamin.peterson | 2008-09-27 18:28:43 -0500 (Sat, 27 Sep 2008) | 1 line clarify a few things ........ r66662 | andrew.kuchling | 2008-09-27 19:15:27 -0500 (Sat, 27 Sep 2008) | 1 line #1579477: mention necessity to flush output before exec'ing ........ r66663 | andrew.kuchling | 2008-09-27 20:08:47 -0500 (Sat, 27 Sep 2008) | 1 line #1415508: Document two functions ........ r66664 | benjamin.peterson | 2008-09-27 20:51:36 -0500 (Sat, 27 Sep 2008) | 1 line better grammar ........ r66665 | benjamin.peterson | 2008-09-27 20:53:29 -0500 (Sat, 27 Sep 2008) | 1 line note the 2to3 -d could be useful for other refactoring ........
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iterable = iter(o)
except TypeError:
Devil merge! Merged revisions 66561,66564,66580,66610,66614,66618,66624-66625,66628-66629,66643,66645,66660-66665 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r66561 | benjamin.peterson | 2008-09-22 17:13:29 -0500 (Mon, 22 Sep 2008) | 1 line clean up docs for platform's linux_distribution and dist functions ........ r66564 | benjamin.peterson | 2008-09-23 08:32:46 -0500 (Tue, 23 Sep 2008) | 1 line mention how to override boolean evaluation ........ r66580 | georg.brandl | 2008-09-24 04:47:55 -0500 (Wed, 24 Sep 2008) | 2 lines Indentation normalization. ........ r66610 | andrew.kuchling | 2008-09-24 12:27:55 -0500 (Wed, 24 Sep 2008) | 1 line Improve wording ........ r66614 | benjamin.peterson | 2008-09-24 17:11:59 -0500 (Wed, 24 Sep 2008) | 4 lines #3950 fix missing scale factors in turtle.py reviewers: Georg, Benjamin ........ r66618 | benjamin.peterson | 2008-09-25 15:35:45 -0500 (Thu, 25 Sep 2008) | 1 line add a NEWs entry for r66614 ........ r66624 | raymond.hettinger | 2008-09-25 18:31:52 -0500 (Thu, 25 Sep 2008) | 1 line Fix namedtuple bug reported by Glenn Linderman. Template did not form correctly if the field names were input in Unicode. ........ r66625 | benjamin.peterson | 2008-09-25 21:58:36 -0500 (Thu, 25 Sep 2008) | 1 line add the beginnings of a C-API 2 -> 3 porting guide ........ r66628 | benjamin.peterson | 2008-09-26 15:52:06 -0500 (Fri, 26 Sep 2008) | 1 line add an 'other options' section ........ r66629 | georg.brandl | 2008-09-26 16:15:21 -0500 (Fri, 26 Sep 2008) | 2 lines typos. ........ r66643 | andrew.kuchling | 2008-09-27 09:12:33 -0500 (Sat, 27 Sep 2008) | 1 line Add a last bunch of items ........ r66645 | benjamin.peterson | 2008-09-27 11:23:55 -0500 (Sat, 27 Sep 2008) | 1 line 2to3's api should be considered unstable ........ r66660 | andrew.kuchling | 2008-09-27 17:54:08 -0500 (Sat, 27 Sep 2008) | 1 line #3510: future-proof text ........ r66661 | benjamin.peterson | 2008-09-27 18:28:43 -0500 (Sat, 27 Sep 2008) | 1 line clarify a few things ........ r66662 | andrew.kuchling | 2008-09-27 19:15:27 -0500 (Sat, 27 Sep 2008) | 1 line #1579477: mention necessity to flush output before exec'ing ........ r66663 | andrew.kuchling | 2008-09-27 20:08:47 -0500 (Sat, 27 Sep 2008) | 1 line #1415508: Document two functions ........ r66664 | benjamin.peterson | 2008-09-27 20:51:36 -0500 (Sat, 27 Sep 2008) | 1 line better grammar ........ r66665 | benjamin.peterson | 2008-09-27 20:53:29 -0500 (Sat, 27 Sep 2008) | 1 line note the 2to3 -d could be useful for other refactoring ........
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pass
else:
return list(iterable)
# Let the base class default method raise the TypeError
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return json.JSONEncoder.default(self, o)
.. method:: encode(o)
Return a JSON string representation of a Python data structure, *o*. For
example::
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>>> 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::
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for chunk in json.JSONEncoder().iterencode(bigobject):
mysocket.write(chunk)
Exceptions
----------
.. exception:: JSONDecodeError(msg, doc, pos)
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:: lineno
The line corresponding to *pos*.
.. attribute:: colno
The column corresponding to *pos*.
.. versionadded:: 3.5
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 requires 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 raises a :exc:`ValueError`
when an initial BOM is 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`) code points 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::
>>> # Neither of these calls raises an exception, but the results are not valid JSON
>>> json.dumps(float('-inf'))
'-Infinity'
>>> json.dumps(float('nan'))
'NaN'
>>> # Same when deserializing
>>> json.loads('-Infinity')
-inf
>>> json.loads('NaN')
nan
In the serializer, the *allow_nan* parameter can be used to alter this
behavior. In the deserializer, the *parse_constant* parameter 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}
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`.
.. _json-commandline:
.. program:: json.tool
Command Line Interface
----------------------
.. module:: json.tool
:synopsis: A command line to validate and pretty-print JSON.
**Source code:** :source:`Lib/json/tool.py`
--------------
The :mod:`json.tool` module provides a simple command line interface to validate
and pretty-print JSON objects.
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If the optional ``infile`` and ``outfile`` arguments are not
specified, :attr:`sys.stdin` and :attr:`sys.stdout` will be used respectively:
.. code-block:: shell-session
$ echo '{"json": "obj"}' | python -m json.tool
{
"json": "obj"
}
$ echo '{1.2:3.4}' | python -m json.tool
Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
.. versionchanged:: 3.5
The output is now in the same order as the input. Use the
:option:`--sort-keys` option to sort the output of dictionaries
alphabetically by key.
Command line options
^^^^^^^^^^^^^^^^^^^^
.. cmdoption:: infile
The JSON file to be validated or pretty-printed:
.. code-block:: shell-session
$ python -m json.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`.
.. cmdoption:: --sort-keys
Sort the output of dictionaries alphabetically by key.
.. versionadded:: 3.5
.. cmdoption:: --no-ensure-ascii
Disable escaping of non-ascii characters, see :func:`json.dumps` for more information.
.. versionadded:: 3.9
.. cmdoption:: --json-lines
Parse every input line as separate JSON object.
.. versionadded:: 3.8
.. cmdoption:: --indent, --tab, --no-indent, --compact
Mutually exclusive options for whitespace control
.. versionadded:: 3.9
.. cmdoption:: -h, --help
Show the help message.
.. rubric:: Footnotes
.. [#rfc-errata] As noted in `the errata for RFC 7159
<https://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.