JSON

JSON简介

JSON（JavaScript Object Notation）是一种由道格拉斯·克罗克福特构想设计、轻量级的数据交换语言，以文字为基础，且易于让人阅读。尽管JSON是Javascript的一个子集，但JSON是独立于语言的文本格式，并且采用了类似于C语言家族的一些习惯。
JSON 数据格式与语言无关，脱胎于 JavaScript，但目前很多编程语言都支持 JSON 格式数据的生成和解析。JSON 的官方 MIME 类型是 application/json，文件扩展名是 .json。

Python中的json模块

json_str = json.dumps(data)  # python--->json
data = json.loads(json_str)  # json--->python

json.dump(data, f)   # python--->json
data = json.load(f)  # json--->python

比如我们要将一个字典写到文件：

dic = {'name': 'lcg', 'age': 18, 'hobby': 'music'}
with open('a.txt', 'w', encoding='utf8') as f:
    f.write(dic)

# 此时会报错
TypeError: write() argument must be str, not dict

这时我们就可以用到json模块

import json

dic = {'name': 'lcg', 'age': 18, 'hobby': 'music'}
with open('a.txt', 'w', encoding='utf8') as f:
    json.dump(dic, f)

或者

import json

dic = {'name': 'lcg', 'age': 18, 'hobby': 'music'}
d = json.dumps(dic)
with open('a.txt', 'w', encoding='utf8') as f:
    f.write(d)

json源码

r"""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.  It is derived from a
version of the externally maintained simplejson library.

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
    >>> from collections import OrderedDict
    >>> mydict = OrderedDict([('4', 5), ('6', 7)])
    >>> json.dumps([1,2,3,mydict], 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
    >>> obj = ['foo', {'bar': ['baz', None, 1.0, 2]}]
    >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]') == obj
    True
    >>> json.loads('"\\"foo\\bar"') == '"foo\x08ar'
    True
    >>> from io import StringIO
    >>> io = StringIO('["streaming API"]')
    >>> json.load(io)[0] == 'streaming API'
    True

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)
    >>> from decimal import Decimal
    >>> json.loads('1.1', parse_float=Decimal) == Decimal('1.1')
    True

Specializing JSON object encoding::

    >>> import json
    >>> def encode_complex(obj):
    ...     if isinstance(obj, complex):
    ...         return [obj.real, obj.imag]
    ...     raise TypeError(repr(obj) + " is not JSON serializable")
    ...
    >>> json.dumps(2 + 1j, default=encode_complex)
    '[2.0, 1.0]'
    >>> json.JSONEncoder(default=encode_complex).encode(2 + 1j)
    '[2.0, 1.0]'
    >>> ''.join(json.JSONEncoder(default=encode_complex).iterencode(2 + 1j))
    '[2.0, 1.0]'


Using json.tool from the shell to validate and pretty-print::

    $ 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 3 (char 2)
"""
__version__ = '2.0.9'
__all__ = [
    'dump', 'dumps', 'load', 'loads',
    'JSONDecoder', 'JSONDecodeError', 'JSONEncoder',
]

__author__ = 'Bob Ippolito <bob@redivi.com>'

from .decoder import JSONDecoder, JSONDecodeError
from .encoder import JSONEncoder
import codecs

_default_encoder = JSONEncoder(
    skipkeys=False,
    ensure_ascii=True,
    check_circular=True,
    allow_nan=True,
    indent=None,
    separators=None,
    default=None,
)

def 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 file-like object).

    If ``skipkeys`` is true then ``dict`` keys that are not basic types
    (``str``, ``int``, ``float``, ``bool``, ``None``) will be skipped
    instead of raising a ``TypeError``.

    If ``ensure_ascii`` is false, then the strings written to ``fp`` can
    contain non-ASCII characters if they appear in strings contained in
    ``obj``. Otherwise, all such characters are escaped in JSON strings.

    If ``check_circular`` is false, then the circular reference check
    for container types will be skipped and a circular reference will
    result in an ``OverflowError`` (or worse).

    If ``allow_nan`` is false, then it will be a ``ValueError`` to
    serialize out of range ``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`` is the most compact
    representation.

    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.

    ``default(obj)`` is a function that should return a serializable version
    of obj or raise TypeError. The default simply raises TypeError.

    If *sort_keys* is true (default: ``False``), then the output of
    dictionaries will be sorted by key.

    To use a custom ``JSONEncoder`` subclass (e.g. one that overrides the
    ``.default()`` method to serialize additional types), specify it with
    the ``cls`` kwarg; otherwise ``JSONEncoder`` is used.

    """
    # cached encoder
    if (not skipkeys and ensure_ascii and
        check_circular and allow_nan and
        cls is None and indent is None and separators is None and
        default is None and not sort_keys and not kw):
        iterable = _default_encoder.iterencode(obj)
    else:
        if cls is None:
            cls = JSONEncoder
        iterable = cls(skipkeys=skipkeys, ensure_ascii=ensure_ascii,
            check_circular=check_circular, allow_nan=allow_nan, indent=indent,
            separators=separators,
            default=default, sort_keys=sort_keys, **kw).iterencode(obj)
    # could accelerate with writelines in some versions of Python, at
    # a debuggability cost
    for chunk in iterable:
        fp.write(chunk)


def 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 ``str``.

    If ``skipkeys`` is true then ``dict`` keys that are not basic types
    (``str``, ``int``, ``float``, ``bool``, ``None``) will be skipped
    instead of raising a ``TypeError``.

    If ``ensure_ascii`` is false, then the return value can contain non-ASCII
    characters if they appear in strings contained in ``obj``. Otherwise, all
    such characters are escaped in JSON strings.

    If ``check_circular`` is false, then the circular reference check
    for container types will be skipped and a circular reference will
    result in an ``OverflowError`` (or worse).

    If ``allow_nan`` is false, then it will be a ``ValueError`` to
    serialize out of range ``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`` is the most compact
    representation.

    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.

    ``default(obj)`` is a function that should return a serializable version
    of obj or raise TypeError. The default simply raises TypeError.

    If *sort_keys* is true (default: ``False``), then the output of
    dictionaries will be sorted by key.

    To use a custom ``JSONEncoder`` subclass (e.g. one that overrides the
    ``.default()`` method to serialize additional types), specify it with
    the ``cls`` kwarg; otherwise ``JSONEncoder`` is used.

    """
    # cached encoder
    if (not skipkeys and ensure_ascii and
        check_circular and allow_nan and
        cls is None and indent is None and separators is None and
        default is None and not sort_keys and not kw):
        return _default_encoder.encode(obj)
    if cls is None:
        cls = JSONEncoder
    return cls(
        skipkeys=skipkeys, ensure_ascii=ensure_ascii,
        check_circular=check_circular, allow_nan=allow_nan, indent=indent,
        separators=separators, default=default, sort_keys=sort_keys,
        **kw).encode(obj)


_default_decoder = JSONDecoder(object_hook=None, object_pairs_hook=None)


def detect_encoding(b):
    bstartswith = b.startswith
    if bstartswith((codecs.BOM_UTF32_BE, codecs.BOM_UTF32_LE)):
        return 'utf-32'
    if bstartswith((codecs.BOM_UTF16_BE, codecs.BOM_UTF16_LE)):
        return 'utf-16'
    if bstartswith(codecs.BOM_UTF8):
        return 'utf-8-sig'

    if len(b) >= 4:
        if not b[0]:
            # 00 00 -- -- - utf-32-be
            # 00 XX -- -- - utf-16-be
            return 'utf-16-be' if b[1] else 'utf-32-be'
        if not b[1]:
            # XX 00 00 00 - utf-32-le
            # XX 00 00 XX - utf-16-le
            # XX 00 XX -- - utf-16-le
            return 'utf-16-le' if b[2] or b[3] else 'utf-32-le'
    elif len(b) == 2:
        if not b[0]:
            # 00 XX - utf-16-be
            return 'utf-16-be'
        if not b[1]:
            # XX 00 - utf-16-le
            return 'utf-16-le'
    # default
    return 'utf-8'


def 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 file-like object containing
    a JSON document) to a Python object.

    ``object_hook`` is an optional function that will be called with the
    result of any object literal decode (a ``dict``). The return value of
    ``object_hook`` will be used instead of the ``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 ``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,
    collections.OrderedDict will remember the order of insertion). If
    ``object_hook`` is also defined, the ``object_pairs_hook`` takes priority.

    To use a custom ``JSONDecoder`` subclass, specify it with the ``cls``
    kwarg; otherwise ``JSONDecoder`` is used.

    """
    return loads(fp.read(),
        cls=cls, object_hook=object_hook,
        parse_float=parse_float, parse_int=parse_int,
        parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)


def loads(s, *, encoding=None, cls=None, object_hook=None, parse_float=None,
        parse_int=None, parse_constant=None, object_pairs_hook=None, **kw):
    """Deserialize ``s`` (a ``str``, ``bytes`` or ``bytearray`` instance
    containing a JSON document) to a Python object.

    ``object_hook`` is an optional function that will be called with the
    result of any object literal decode (a ``dict``). The return value of
    ``object_hook`` will be used instead of the ``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 ``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,
    collections.OrderedDict will remember the order of insertion). If
    ``object_hook`` is also defined, the ``object_pairs_hook`` takes priority.

    ``parse_float``, if specified, will be called with the string
    of every JSON float to be decoded. By default this is equivalent to
    float(num_str). This can be used to use another datatype or parser
    for JSON floats (e.g. 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. 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.

    To use a custom ``JSONDecoder`` subclass, specify it with the ``cls``
    kwarg; otherwise ``JSONDecoder`` is used.

    The ``encoding`` argument is ignored and deprecated.

    """
    if isinstance(s, str):
        if s.startswith('\ufeff'):
            raise JSONDecodeError("Unexpected UTF-8 BOM (decode using utf-8-sig)",
                                  s, 0)
    else:
        if not isinstance(s, (bytes, bytearray)):
            raise TypeError('the JSON object must be str, bytes or bytearray, '
                            'not {!r}'.format(s.__class__.__name__))
        s = s.decode(detect_encoding(s), 'surrogatepass')

    if (cls is None and object_hook is None and
            parse_int is None and parse_float is None and
            parse_constant is None and object_pairs_hook is None and not kw):
        return _default_decoder.decode(s)
    if cls is None:
        cls = JSONDecoder
    if object_hook is not None:
        kw['object_hook'] = object_hook
    if object_pairs_hook is not None:
        kw['object_pairs_hook'] = object_pairs_hook
    if parse_float is not None:
        kw['parse_float'] = parse_float
    if parse_int is not None:
        kw['parse_int'] = parse_int
    if parse_constant is not None:
        kw['parse_constant'] = parse_constant
    return cls(**kw).decode(s)

总结：

序列化 dumps() ：encoding，把一个python队形编码转化成JSON字符串，JSON字符串是字符串
反序列化 loads() ：decoding，把JSON格式字符串解码转换为python数据对象，即为字典对象

import json

data = {
    'name': 'lcg',
    'age': 18,
    'hobby': 'music'
}

# 将一个Python数据结构转换为JSON：
json_str = json.dumps(data)

# 将一个JSON编码的字符串转换回一个Python数据结构
data = json.loads(json_str)

# 如果你要处理的是文件而不是字符串,你可以使用 json.dump() 和 json.load() 来编码和解码JSON数据
# ---->JSON
with open('data.json', 'w') as f:
    json.dump(data, f)

# ---->back
with open('data.json', 'r') as f:
    data = json.load(f)

JavaScript中的json

合格的json对象：

["one", "two", "three"]

{ "one": 1, "two": 2, "three": 3 }

{"names": ["张三", "李四"] }

[ { "name": "张三"}, {"name": "李四"} ]　

不合格的json对象：

{ name: "张三", 'age': 32 }                     // 属性名必须使用双引号

[32, 64, 128, 0xFFF]                           // 不能使用十六进制值

{ "name": "张三", "age": undefined }            // 不能使用undefined

{ "name": "张三",
  "birthday": new Date('Fri, 26 Aug 2011 07:13:10 GMT'),
  "getName":  function() {return this.name;}    // 不能使用函数和日期对象
} 　

stringify与parse方法

JSON.parse() 用于将一个 JSON 字符串转换为 JavaScript 对象　

console.log(JSON.parse('{"name":"lcg"}'));
console.log(JSON.parse('{name:"lcg"}')) ;   // 错误
console.log(JSON.parse('[12,undefined]')) ; // 错误

JSON.stringify() 用于将 JavaScript 值转换为 JSON 字符串。

console.log(JSON.stringify({'name':"lcg"})) ;

 

参考：http://python3-cookbook.readthedocs.io/zh_CN/latest/c06/p02_read-write_json_data.html

参考：http://www.cnblogs.com/yuanchenqi/articles/7638956.html