764 lines
28 KiB
ReStructuredText
764 lines
28 KiB
ReStructuredText
: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::
|
|
|
|
>>> 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))
|
|
{
|
|
"4": 5,
|
|
"6": 7
|
|
}
|
|
|
|
Decoding JSON::
|
|
|
|
>>> 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`::
|
|
|
|
>>> 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)
|
|
...
|
|
>>> json.dumps(2 + 1j, cls=ComplexEncoder)
|
|
'[2.0, 1.0]'
|
|
>>> ComplexEncoder().encode(2 + 1j)
|
|
'[2.0, 1.0]'
|
|
>>> list(ComplexEncoder().iterencode(2 + 1j))
|
|
['[2.0', ', 1.0', ']']
|
|
|
|
|
|
Using :mod:`json.tool` from the shell to validate and pretty-print:
|
|
|
|
.. 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)
|
|
|
|
See :ref:`json-commandline` for detailed documentation.
|
|
|
|
.. 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
|
|
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
|
|
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
|
|
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
|
|
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 |
|
|
+---------------+-------------------+
|
|
| 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
|
|
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::
|
|
|
|
def default(self, o):
|
|
try:
|
|
iterable = iter(o)
|
|
except TypeError:
|
|
pass
|
|
else:
|
|
return list(iterable)
|
|
# Let the base class default method raise the TypeError
|
|
return json.JSONEncoder.default(self, o)
|
|
|
|
|
|
.. method:: encode(o)
|
|
|
|
Return a JSON string representation of a Python data structure, *o*. For
|
|
example::
|
|
|
|
>>> 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 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.
|
|
|
|
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.
|