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| -rw-r--r-- | Doc/library/json.rst | 397 | ||||
| -rw-r--r-- | Doc/library/netdata.rst | 1 | ||||
| -rw-r--r-- | Doc/whatsnew/2.6.rst | 26 |
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diff --git a/Doc/library/json.rst b/Doc/library/json.rst new file mode 100644 index 0000000..a0a62d1 --- /dev/null +++ b/Doc/library/json.rst @@ -0,0 +1,397 @@ +: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. + + +.. 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[, **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(fp)(encoding)``, 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 decode (a :class:`dict`). The return value of + *object_hook* will be used instead of the :class:`dict`. This feature can be used + to implement custom decoders (e.g. JSON-RPC class hinting). + + *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. 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[, **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:`dump`. + + +Encoders and decoders +--------------------- + +.. class:: JSONDecoder([encoding[, object_hook[, parse_float[, parse_int[, parse_constant[, strict]]]]]]) + + 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). + + *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. + + + .. 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`` (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 *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) diff --git a/Doc/library/netdata.rst b/Doc/library/netdata.rst index add01d2..2f27189 100644 --- a/Doc/library/netdata.rst +++ b/Doc/library/netdata.rst @@ -12,6 +12,7 @@ on the Internet. .. toctree:: email.rst + json.rst mailcap.rst mailbox.rst mhlib.rst diff --git a/Doc/whatsnew/2.6.rst b/Doc/whatsnew/2.6.rst index 8bd0c19..1af6f73 100644 --- a/Doc/whatsnew/2.6.rst +++ b/Doc/whatsnew/2.6.rst @@ -1210,6 +1210,7 @@ Mullender that was in Python's :file:`Demo/classes/` directory for a long time. This implementation was significantly updated by Jeffrey Yasskin. + Other Language Changes ====================== @@ -2146,6 +2147,31 @@ complete list of changes, or look through the CVS logs for all the details. .. ====================================================================== .. whole new modules get described in subsections here +The :mod:`json` module +---------------------- + +The new :mod:`json` module supports the encoding and decoding of Python types in +JSON (Javascript Object Notation). JSON is a lightweight interchange format +often used in web applications. For more information about JSON, see +http://www.json.org. + +:mod:`json` comes with support for decoding and encoding most builtin Python +types. The following example encodes and decodes a dictionary:: + + >>> import json + >>> data = {"spam" : "foo", "parrot" : 42} + >>> in_json = json.dumps(data) # Encode the data + >>> in_json + '{"parrot": 42, "spam": "foo"}' + >>> json.loads(in_json) # Decode into a Python object + {"spam" : "foo", "parrot" : 42} + +It is also possible to write your own decoders and encoders to support more +types. Pretty-printing of the JSON strings is also supported. + +:mod:`json` (originally called simplejson) was written by Bob Ippolito. + + Improved SSL Support -------------------------------------------------- |