
"json" --- JSON encoder and decoder
***********************************

JSON (JavaScript Object Notation), specified by **RFC 4627**, is a
lightweight data interchange format based on a subset of JavaScript
syntax (ECMA-262 3rd edition).

"json" exposes an API familiar to users of the standard library
"marshal" and "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 "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 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)

Note: JSON is a subset of YAML 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.


Basic Usage
===========

json.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*) using this *conversion
   table*.

   If *skipkeys* is "True" (default: "False"), then dict keys that are
   not of a basic type ("str", "int", "float", "bool", "None") will be
   skipped instead of raising a "TypeError".

   The "json" module always produces "str" objects, not "bytes"
   objects. Therefore, "fp.write()" must support "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 "OverflowError" (or worse).

   If *allow_nan* is "False" (default: "True"), 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 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.

   Changed in version 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.

   Changed in version 3.4: Use "(',', ': ')" as default if *indent* is
   not "None".

   *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.

json.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" using this *conversion
   table*.  The arguments have the same meaning as in "dump()".

   Note: Unlike "pickle" and "marshal", JSON is not a framed
     protocol, so trying to serialize multiple objects with repeated
     calls to "dump()" using the same *fp* will result in an invalid
     JSON file.

   Note: Keys in key/value pairs of JSON are always of the type
     "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.

json.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 using this
   *conversion table*.

   *object_hook* is an optional function that will be called with the
   result of any object literal decoded (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.

   Changed in version 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. "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.

   Changed in version 3.1: *parse_constant* doesn't get called on
   'null', 'true', 'false' anymore.

   To use a custom "JSONDecoder" subclass, specify it with the "cls"
   kwarg; otherwise "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
   "ValueError" will be raised.

json.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" instance containing a JSON document) to a
   Python object using this *conversion table*.

   The other arguments have the same meaning as in "load()", except
   *encoding* which is ignored and deprecated.

   If the data being deserialized is not a valid JSON document, a
   "ValueError" will be raised.


Encoders and Decoders
=====================

class class json.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            | 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 "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
   "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.

   Changed in version 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. "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'", "'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'".

   If the data being deserialized is not a valid JSON document, a
   "ValueError" will be raised.

   decode(s)

      Return the Python representation of *s* (a "str" instance
      containing a JSON document)

   raw_decode(s)

      Decode a JSON document from *s* (a "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 class json.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:

   +------------------------------------------+-----------------+
   | Python                                   | JSON            |
   +==========================================+=================+
   | dict                                     | object          |
   +------------------------------------------+-----------------+
   | list, tuple                              | array           |
   +------------------------------------------+-----------------+
   | str                                      | string          |
   +------------------------------------------+-----------------+
   | int, float, int- & float-derived Enums   | number          |
   +------------------------------------------+-----------------+
   | True                                     | true            |
   +------------------------------------------+-----------------+
   | False                                    | false           |
   +------------------------------------------+-----------------+
   | None                                     | null            |
   +------------------------------------------+-----------------+

   Changed in version 3.4: Added support for int- and float-derived
   Enum classes.

   To extend this to recognize other objects, subclass and implement a
   "default()" method with another method that returns a serializable
   object for "o" if possible, otherwise it should call the superclass
   implementation (to raise "TypeError").

   If *skipkeys* is "False" (the default), then it is a "TypeError" to
   attempt encoding of keys that are not str, int, 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 "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 "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.

   Changed in version 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.

   Changed in version 3.4: Use "(',', ': ')" as default if *indent* is
   not "None".

   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 "TypeError".

   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 "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)

   encode(o)

      Return a JSON string representation of a Python data structure,
      *o*.  For example:

         >>> json.JSONEncoder().encode({"foo": ["bar", "baz"]})
         '{"foo": ["bar", "baz"]}'

   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)


Standard Compliance
===================

The JSON format is specified by **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:

* Top-level non-object, non-array values are accepted and output;

* 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 recommends that JSON be represented using either UTF-8,
UTF-16, or UTF-32, with UTF-8 being the default.

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 "Unicode
strings", and thus does not otherwise address the issue of character
encodings.


Top-level Non-Object, Non-Array Values
--------------------------------------

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)
   '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 = "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.


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 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)
   {'x': 3}

The *object_pairs_hook* parameter can be used to alter this behavior.
