425 lines
17 KiB
ReStructuredText
425 lines
17 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>
|
|
.. versionadded:: 2.6
|
|
|
|
`JSON (JavaScript Object Notation) <http://json.org>`_ is a subset of JavaScript
|
|
syntax (ECMA-262 3rd edition) used as a lightweight data interchange format.
|
|
|
|
:mod:`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(u'\u1234')
|
|
"\u1234"
|
|
>>> print json.dumps('\\')
|
|
"\\"
|
|
>>> print json.dumps({"c": 0, "b": 0, "a": 0}, sort_keys=True)
|
|
{"a": 0, "b": 0, "c": 0}
|
|
>>> from StringIO import StringIO
|
|
>>> io = StringIO()
|
|
>>> json.dump(['streaming API'], io)
|
|
>>> io.getvalue()
|
|
'["streaming API"]'
|
|
|
|
Compact encoding::
|
|
|
|
>>> import 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]}]')
|
|
[u'foo', {u'bar': [u'baz', None, 1.0, 2]}]
|
|
>>> json.loads('"\\"foo\\bar"')
|
|
u'"foo\x08ar'
|
|
>>> from StringIO import StringIO
|
|
>>> io = StringIO('["streaming API"]')
|
|
>>> json.load(io)
|
|
[u'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]
|
|
... return json.JSONEncoder.default(self, obj)
|
|
...
|
|
>>> 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', ']']
|
|
|
|
|
|
.. highlight:: none
|
|
|
|
Using json.tool from the shell to validate and pretty-print::
|
|
|
|
$ echo '{"json":"obj"}' | python -mjson.tool
|
|
{
|
|
"json": "obj"
|
|
}
|
|
$ echo '{ 1.2:3.4}' | python -mjson.tool
|
|
Expecting property name: line 1 column 2 (char 2)
|
|
|
|
.. highlight:: python
|
|
|
|
.. note::
|
|
|
|
The JSON produced by this module's default settings is a subset of
|
|
YAML, so it may be used as a serializer for that as well.
|
|
|
|
|
|
Basic Usage
|
|
-----------
|
|
|
|
.. function:: dump(obj, fp[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, **kw]]]]]]]]]])
|
|
|
|
Serialize *obj* as a JSON formatted stream to *fp* (a ``.write()``-supporting
|
|
file-like object).
|
|
|
|
If *skipkeys* is ``True`` (default: ``False``), then dict keys that are not
|
|
of a basic type (:class:`str`, :class:`unicode`, :class:`int`, :class:`long`,
|
|
:class:`float`, :class:`bool`, ``None``) will be skipped instead of raising a
|
|
:exc:`TypeError`.
|
|
|
|
If *ensure_ascii* is ``False`` (default: ``True``), then some chunks written
|
|
to *fp* may be :class:`unicode` instances, subject to normal Python
|
|
:class:`str` to :class:`unicode` coercion rules. Unless ``fp.write()``
|
|
explicitly understands :class:`unicode` (as in :func:`codecs.getwriter`) this
|
|
is likely to cause an error.
|
|
|
|
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, instead of
|
|
using the JavaScript equivalents (``NaN``, ``Infinity``, ``-Infinity``).
|
|
|
|
If *indent* is a non-negative integer, then JSON array elements and object
|
|
members will be pretty-printed with that indent level. An indent level of 0
|
|
will only insert newlines. ``None`` (the default) selects the most compact
|
|
representation.
|
|
|
|
If *separators* is an ``(item_separator, dict_separator)`` tuple, then it
|
|
will be used instead of the default ``(', ', ': ')`` separators. ``(',',
|
|
':')`` is the most compact JSON representation.
|
|
|
|
*encoding* is the character encoding for str instances, default is UTF-8.
|
|
|
|
*default(obj)* is a function that should return a serializable version of
|
|
*obj* or raise :exc:`TypeError`. The default simply raises :exc:`TypeError`.
|
|
|
|
To use a custom :class:`JSONEncoder` subclass (e.g. one that overrides the
|
|
:meth:`default` method to serialize additional types), specify it with the
|
|
*cls* kwarg; otherwise :class:`JSONEncoder` is used.
|
|
|
|
|
|
.. function:: dumps(obj[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, **kw]]]]]]]]]])
|
|
|
|
Serialize *obj* to a JSON formatted :class:`str`.
|
|
|
|
If *ensure_ascii* is ``False``, then the return value will be a
|
|
:class:`unicode` instance. The other arguments have the same meaning as in
|
|
:func:`dump`.
|
|
|
|
|
|
.. function:: load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])
|
|
|
|
Deserialize *fp* (a ``.read()``-supporting file-like object containing a JSON
|
|
document) to a Python object.
|
|
|
|
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(encoding)(fp)``, or simply decoded
|
|
to a :class:`unicode` object and passed to :func:`loads`.
|
|
|
|
*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 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 that
|
|
rely on the order that the key and value pairs are decoded (for example,
|
|
:func:`collections.OrderedDict` will remember the order of insertion). If
|
|
*object_hook* is also defined, the *object_pairs_hook* takes priority.
|
|
|
|
.. versionchanged:: 2.7
|
|
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'``, ``'null'``, ``'true'``,
|
|
``'false'``. This can be used to raise an exception if invalid JSON numbers
|
|
are encountered.
|
|
|
|
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.
|
|
|
|
|
|
.. function:: loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])
|
|
|
|
Deserialize *s* (a :class:`str` or :class:`unicode` instance containing a JSON
|
|
document) to a Python object.
|
|
|
|
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.
|
|
|
|
The other arguments have the same meaning as in :func:`load`.
|
|
|
|
|
|
Encoders and decoders
|
|
---------------------
|
|
|
|
.. class:: JSONDecoder([encoding[, object_hook[, parse_float[, parse_int[, parse_constant[, strict[, object_pairs_hook]]]]]]])
|
|
|
|
Simple JSON decoder.
|
|
|
|
Performs the following translations in decoding by default:
|
|
|
|
+---------------+-------------------+
|
|
| JSON | Python |
|
|
+===============+===================+
|
|
| object | dict |
|
|
+---------------+-------------------+
|
|
| array | list |
|
|
+---------------+-------------------+
|
|
| string | unicode |
|
|
+---------------+-------------------+
|
|
| number (int) | int, long |
|
|
+---------------+-------------------+
|
|
| number (real) | float |
|
|
+---------------+-------------------+
|
|
| true | True |
|
|
+---------------+-------------------+
|
|
| false | False |
|
|
+---------------+-------------------+
|
|
| null | None |
|
|
+---------------+-------------------+
|
|
|
|
It also understands ``NaN``, ``Infinity``, and ``-Infinity`` as their
|
|
corresponding ``float`` values, which is outside the JSON spec.
|
|
|
|
*encoding* determines the encoding used to interpret any :class:`str` objects
|
|
decoded by this instance (UTF-8 by default). It has no effect when decoding
|
|
:class:`unicode` objects.
|
|
|
|
Note that currently only encodings that are a superset of ASCII work, strings
|
|
of other encodings should be passed in as :class:`unicode`.
|
|
|
|
*object_hook*, 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 that rely on the order
|
|
that the key and value pairs are decoded (for example,
|
|
:func:`collections.OrderedDict` will remember the order of insertion). If
|
|
*object_hook* is also defined, the *object_pairs_hook* takes priority.
|
|
|
|
.. versionchanged:: 2.7
|
|
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'``, ``'null'``, ``'true'``,
|
|
``'false'``. 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'``.
|
|
|
|
|
|
.. method:: decode(s)
|
|
|
|
Return the Python representation of *s* (a :class:`str` or
|
|
:class:`unicode` instance containing a JSON document)
|
|
|
|
.. method:: raw_decode(s)
|
|
|
|
Decode a JSON document from *s* (a :class:`str` or :class:`unicode`
|
|
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[, ensure_ascii[, check_circular[, allow_nan[, sort_keys[, indent[, separators[, encoding[, default]]]]]]]]])
|
|
|
|
Extensible JSON encoder for Python data structures.
|
|
|
|
Supports the following objects and types by default:
|
|
|
|
+-------------------+---------------+
|
|
| Python | JSON |
|
|
+===================+===============+
|
|
| dict | object |
|
|
+-------------------+---------------+
|
|
| list, tuple | array |
|
|
+-------------------+---------------+
|
|
| str, unicode | string |
|
|
+-------------------+---------------+
|
|
| int, long, float | number |
|
|
+-------------------+---------------+
|
|
| True | true |
|
|
+-------------------+---------------+
|
|
| False | false |
|
|
+-------------------+---------------+
|
|
| None | null |
|
|
+-------------------+---------------+
|
|
|
|
To extend this to recognize other objects, subclass and implement a
|
|
:meth:`default` method with another method that returns a serializable object
|
|
for ``o`` if possible, otherwise it should call the superclass implementation
|
|
(to raise :exc:`TypeError`).
|
|
|
|
If *skipkeys* is ``False`` (the default), then it is a :exc:`TypeError` to
|
|
attempt encoding of keys that are not str, int, long, float or None. If
|
|
*skipkeys* is ``True``, such items are simply skipped.
|
|
|
|
If *ensure_ascii* is ``True`` (the default), the output is guaranteed to be
|
|
:class:`str` objects with all incoming unicode characters escaped. If
|
|
*ensure_ascii* is ``False``, the output will be a unicode object.
|
|
|
|
If *check_circular* is ``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 (it is ``None`` by default), then JSON
|
|
array elements and object members will be pretty-printed with that indent
|
|
level. An indent level of 0 will only insert newlines. ``None`` is the most
|
|
compact representation.
|
|
|
|
If specified, *separators* should be an ``(item_separator, key_separator)``
|
|
tuple. The default is ``(', ', ': ')``. To get the most compact JSON
|
|
representation, you should specify ``(',', ':')`` to eliminate whitespace.
|
|
|
|
If specified, *default* is a function that gets called for objects that can't
|
|
otherwise be serialized. It should return a JSON encodable version of the
|
|
object or raise a :exc:`TypeError`.
|
|
|
|
If *encoding* is not ``None``, then all input strings will be transformed
|
|
into unicode using that encoding prior to JSON-encoding. The default is
|
|
UTF-8.
|
|
|
|
|
|
.. method:: default(o)
|
|
|
|
Implement this method in a subclass such that it returns a serializable
|
|
object for *o*, or calls the base implementation (to raise a
|
|
:exc:`TypeError`).
|
|
|
|
For example, to support arbitrary iterators, you could implement default
|
|
like this::
|
|
|
|
def default(self, o):
|
|
try:
|
|
iterable = iter(o)
|
|
except TypeError:
|
|
pass
|
|
else:
|
|
return list(iterable)
|
|
return JSONEncoder.default(self, o)
|
|
|
|
|
|
.. method:: encode(o)
|
|
|
|
Return a JSON string representation of a Python data structure, *o*. For
|
|
example::
|
|
|
|
>>> 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)
|