2.6 版新增。
JSON (JavaScript 对象表示法) ，指定通过 RFC 4627 , is a lightweight data interchange format based on a subset of JavaScript syntax ( ECMA-262 3rd edition ).
json 暴露用户熟悉的 API 标准库 marshal and pickle 模块。
编码基本 Python 对象层次结构：
>>> 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"]'
紧凑编码：
>>> import json >>> json.dumps([1,2,3,{'4': 5, '6': 7}], separators=(',',':')) '[1,2,3,{"4":5,"6":7}]'
美化打印：
>>> import json >>> print json.dumps({'4': 5, '6': 7}, sort_keys=True, ... indent=4, separators=(',', ': ')) { "4": 5, "6": 7 }
解码 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']
专攻 JSON 对象解码：
>>> 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')
延伸 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) ... >>> 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 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 enclosed in double quotes: line 1 column 2 (char 1)
注意
JSON 是子集对于 YAML 1.2。由此模块的默认设置产生的 JSON (尤其，默认 separators 值) 还是 YAML 1.0 和 1.1 的子集。因此，此模块也可以用作 YAML 序列化器。
序列化 obj 作为 JSON (JavaScript 对象表示法) 格式化流到 fp ( .write() 支持 像文件对象 ) 使用此 转换表 .
若 skipkeys is True (default: False )，则不是基本类型的字典键 ( str , unicode , int , long , float , bool , None ) 会被跳过而不是引发 TypeError .
若 ensure_ascii is True (the default), all non-ASCII characters in the output are escaped with \uXXXX sequences, and the result is a str instance consisting of ASCII characters only. If ensure_ascii is False , some chunks written to fp 可以是 unicode instances. This usually happens because the input contains unicode strings or the encoding parameter is used. Unless fp.write() explicitly understands unicode (as in codecs.getwriter() ) this is likely to cause an error.
若 check_circular is False (default: True )，那么将跳过容器类型的循环引用校验，且循环引用会导致 OverflowError (或更糟)。
若 allow_nan is False (default: True )，那么它将是 ValueError 序列化超出范围的 float 值 ( nan , inf , -inf ) in strict compliance of the JSON specification, instead of using the JavaScript equivalents ( NaN , Infinity , -Infinity ).
若 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, or negative, will only insert newlines. None (the default) selects the most compact representation.
注意
Since the default item separator is ', ' , the output might include trailing whitespace when indent is specified. You can use separators=(',', ': ') to avoid this.
若 separators 是 (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 TypeError . The default simply raises TypeError .
若 sort_keys is True (default: False )，那么将按键排序字典的输出。
要使用自定义 JSONEncoder 子类 (如：覆写 default() 方法以序列化额外类型)，指定它采用 cls 关键词自变量；否则 JSONEncoder 被使用。
注意
不像 pickle and marshal , JSON is not a framed protocol so trying to serialize more objects with repeated calls to dump() and the same fp 将导致无效 JSON 文件。
序列化 obj 到 JSON 格式化 str 使用此 转换表 。若 ensure_ascii is False , the result may contain non-ASCII characters and the return value may be a unicode 实例。
The arguments have the same meaning as in dump() .
注意
JSON 键/值对中的键始终是类型 str 。当将字典转换成 JSON 时，字典的所有键都被强迫为字符串。因此，若字典被转换成 JSON 然后再转换回字典，字典可能不等于原始字典。也就是说， loads(dumps(x)) != x 若 x 拥有非字符串键。
反序列化 fp ( .read() 支持 像文件对象 包含 JSON 文档) 成 Python 对象使用此 转换表 .
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 unicode object and passed to loads() .
object_hook 是将被调用的可选函数采用任何对象文字解码结果 ( dict )。返回值的 object_hook 将被使用而不是 dict 。可以使用此特征实现自定义解码器 (如 JSON-RPC 类提示)。
object_pairs_hook 是将被调用的可选函数采用任何对象文字按有序对列表解码的结果。返回值的 object_pairs_hook 将被使用而不是 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 也有定义， object_pairs_hook 优先。
2.7 版改变： 添加支持 object_pairs_hook .
parse_float 若指定，将被调用采用每个要解码的 JSON 浮点字符串。默认情况下，这相当于 float(num_str) 。可以使用这对 JSON 浮点使用另一数据类型或剖析器 (如 decimal.Decimal ).
parse_int 若指定，将被调用采用要被解码的每个 JSON int 字符串。默认情况下，这相当于 int(num_str) 。可以使用这对 JSON 整数使用另一数据类型或剖析器 (如 float ).
parse_constant 若指定，将被调用采用下列字符串之一： '-Infinity' , 'Infinity' , 'NaN' 。可以使用这引发异常，若遭遇无效 JSON 数字。
2.7 版改变： parse_constant 不再按 null、True、False 被调用。
要使用自定义 JSONDecoder 子类，指定它采用 cls 关键词自变量；否则 JSONDecoder 被使用。额外关键词自变量将被传递给类构造函数。
反序列化 s ( str or unicode 实例包含 JSON 文档) 成 Python 对象使用此 转换表 .
若 s 是 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 unicode 首先。
其它自变量拥有相同含义如在 load() .
简单 JSON 解码器。
默认情况下，当解码时履行下列翻译：
| JSON | Python |
|---|---|
| 对象 | dict |
| array | list |
| string | unicode |
| 数字 (int) | int, long |
| 数字 (real) | float |
| true | True |
| false | False |
| null | None |
它还理解 NaN , Infinity ，和 -Infinity 作为其相应 float 值，这有超出 JSON 规范。
encoding determines the encoding used to interpret any str objects decoded by this instance (UTF-8 by default). It has no effect when decoding unicode 对象。
Note that currently only encodings that are a superset of ASCII work, strings of other encodings should be passed in as unicode .
object_hook 若指定，将被调用采用每个 JSON 对象的解码结果，且会使用其返回值替代给定 dict 。这可以用于提供自定义反序列化 (如：支持 JSON-RPC 类提示)。
object_pairs_hook 若指定将被调用采用按对有序列表解码的每个 JSON 对象结果。返回值的 object_pairs_hook 将被使用而不是 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 也有定义， object_pairs_hook 优先。
2.7 版改变： 添加支持 object_pairs_hook .
parse_float 若指定，将被调用采用每个要解码的 JSON 浮点字符串。默认情况下，这相当于 float(num_str) 。可以使用这对 JSON 浮点使用另一数据类型或剖析器 (如 decimal.Decimal ).
parse_int 若指定，将被调用采用要被解码的每个 JSON int 字符串。默认情况下，这相当于 int(num_str) 。可以使用这对 JSON 整数使用另一数据类型或剖析器 (如 float ).
parse_constant 若指定，将被调用采用下列字符串之一： '-Infinity' , 'Infinity' , 'NaN' , 'null' , 'true' , 'false' 。可以使用这引发异常，若遭遇无效 JSON 数字。
若 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' .
若要反序列化的数据不是有效 JSON 文档， ValueError 会被引发。
解码 JSON 文档从 s ( str or unicode 开头采用 JSON 文档) 并返回 2 元素元组的 Python 表示和索引在 s 在哪里结束文档。
这可以用于从末尾可能拥有外来数据的字符串解码 JSON 文档。
用于 Python 数据结构的可扩展 JSON 编码器。
默认情况下，支持下列对象和类型：
| Python | JSON |
|---|---|
| dict | 对象 |
| list, tuple | array |
| str, unicode | string |
| int, long, float | 编号 |
| True | true |
| False | false |
| None | null |
要扩展这以识别其它对象，子类并实现 default() 方法采用另一方法返回可序列化对象对于 o 若可能的话，否则，应该调用超类实现 (会引发 TypeError ).
若 skipkeys is False (the default), then it is a TypeError to attempt encoding of keys that are not str, int, long, float or None. If skipkeys is True , such items are simply skipped.
若 ensure_ascii is True (the default), all non-ASCII characters in the output are escaped with \uXXXX sequences, and the results are str instances consisting of ASCII characters only. If ensure_ascii is False , a result may be a unicode instance. This usually happens if the input contains unicode strings or the encoding parameter is used.
若 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 OverflowError )。否则，不发生这种校验。
若 allow_nan is True (默认)，那么 NaN , Infinity ，和 -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 ValueError to encode such floats.
若 sort_keys is True (默认 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.
若 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.
注意
Since the default item separator is ', ' , the output might include trailing whitespace when indent is specified. You can use separators=(',', ': ') to avoid this.
若指定， separators 应该为 (item_separator, key_separator) 元组。默认为 (', ', ': ') . To get the most compact JSON representation, you should specify (',', ':') 以消除空白。
若指定， 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 TypeError .
若 encoding 不是 None , then all input strings will be transformed into unicode using that encoding prior to JSON-encoding. The default is UTF-8.
Implement this method in a subclass such that it returns a serializable object for o ，或调用基实现 (以引发 TypeError ).
例如，为支持任意迭代器，默认实现可以像这样：
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 JSONEncoder.default(self, o)
返回 JSON 字符串表示为 Python 数据结构 o 。例如：
>>> JSONEncoder().encode({"foo": ["bar", "baz"]}) '{"foo": ["bar", "baz"]}'
编码给定对象 o ，并产生可用的每个字符串表示。例如：
for chunk in JSONEncoder().iterencode(bigobject): mysocket.write(chunk)
JSON 格式的指定通过 RFC 4627 . This section details this module’s level of compliance with the RFC. For simplicity, JSONEncoder and 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:
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.
The RFC recommends that JSON be represented using either UTF-8, UTF-16, or UTF-32, with UTF-8 being the default. Accordingly, this module uses UTF-8 as the default for its encoding 参数。
This module’s deserializer only directly works with ASCII-compatible encodings; UTF-16, UTF-32, and other ASCII-incompatible encodings require the use of workarounds described in the documentation for the deserializer’s encoding 参数。
The RFC also non-normatively describes a limited encoding detection technique for JSON texts; this module’s deserializer does not implement this or any other kind of encoding detection.
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.
The RFC specifies that the top-level value of a JSON text must be either a JSON object or array (Python dict or list ). This module’s deserializer also accepts input texts consisting solely of a JSON null, boolean, number, or string value:
>>> just_a_json_string = '"spam and eggs"' # Not by itself a valid JSON text >>> json.loads(just_a_json_string) u'spam and eggs'
This module itself does not include a way to request that such input texts be regarded as illegal. Likewise, this module’s serializer also accepts single Python None , bool , numeric, and str values as input and will generate output texts consisting solely of a top-level JSON null, boolean, number, or string value without raising an exception:
>>> neither_a_list_nor_a_dict = u"spam and eggs" >>> json.dumps(neither_a_list_nor_a_dict) # The result is not a valid JSON text '"spam and eggs"'
This module’s serializer does not itself include a way to enforce the aforementioned constraint.
The RFC does not permit the representation of infinite or NaN number values. Despite that, by default, this module accepts and outputs Infinity , -Infinity ，和 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
在序列化器中， allow_nan 参数可用于更改此行为。在反序列化器中， parse_constant 参数可用于更改此行为。
The RFC specifies that the names within a JSON object should be unique, but does not specify 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) {u'x': 3}
The object_pairs_hook 参数可用于更改此行为。