### Navigation

- index
- simplejson v2.1.1 documentation »

# `simplejson` — JSON encoder and decoder

JSON (JavaScript Object Notation) <http://json.org> is a subset of JavaScript syntax (ECMA-262 3rd edition) used as a lightweight data interchange format.

`simplejson` exposes an API familiar to users of the standard library `marshal` and `pickle` modules. It is the externally maintained version of the `json` library contained in Python 2.6, but maintains compatibility with Python 2.5 and (currently) has significant performance advantages, even without using the optional C extension for speedups.

Encoding basic Python object hierarchies:

    >>> import simplejson as 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 simplejson as json
    >>> json.dumps([1,2,3,{'4': 5, '6': 7}], separators=(',',':'))
    '[1,2,3,{"4":5,"6":7}]'

Pretty printing:

    >>> import simplejson as json
    >>> s = json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4 * ' ')
    >>> print '\n'.join([l.rstrip() for l in  s.splitlines()])
    {
        "4": 5,
        "6": 7
    }

Decoding JSON:

    >>> import simplejson as json
    >>> obj = [u'foo', {u'bar': [u'baz', None, 1.0, 2]}]
    >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]') == obj
    True
    >>> json.loads('"\\"foo\\bar"') == u'"foo\x08ar'
    True
    >>> from StringIO import StringIO
    >>> io = StringIO('["streaming API"]')
    >>> json.load(io)[0] == 'streaming API'
    True

Using Decimal instead of float:

    >>> import simplejson as json
    >>> from decimal import Decimal
    >>> json.loads('1.1', use_decimal=True) == Decimal('1.1')
    True
    >>> json.dumps(Decimal('1.1'), use_decimal=True) == '1.1'
    True

Specializing JSON object decoding:

    >>> import simplejson as 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.Decimal('1.1')
    True

Specializing JSON object encoding:

    >>> import simplejson as json
    >>> def encode_complex(obj):
    ...     if isinstance(obj, complex):
    ...         return [obj.real, obj.imag]
    ...     raise TypeError(repr(o) + " 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 `simplejson.tool` from the shell to validate and pretty-print:

    $ echo '{"json":"obj"}' | python -m simplejson.tool
    {
        "json": "obj"
    }
    $ echo '{ 1.2:3.4}' | python -m simplejson.tool
    Expecting property name: line 1 column 2 (char 2)

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

`simplejson.``dump`(obj, fp[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, use_decimal[, **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 (`str`, `unicode`, `int`, `long`, `float`, `bool`, `None`) will be skipped instead of raising a `TypeError`.

  If ensure_ascii is false (default: `True`), then some chunks written to fp may be `unicode` instances, subject to normal Python `str` to `unicode` coercion rules. Unless `fp.write()` explicitly understands `unicode` (as in `codecs.getwriter()`) this is likely to cause an error. It’s best to leave the default settings, because they are safe and it is highly optimized.

  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. If allow_nan is true, their JavaScript equivalents will be used (`NaN`, `Infinity`, `-Infinity`).

  If indent is a string, then JSON array elements and object members will be pretty-printed with a newline followed by that string repeated for each level of nesting. `None` (the default) selects the most compact representation without any newlines. For backwards compatibility with versions of simplejson earlier than 2.1.0, an integer is also accepted and is converted to a string with that many spaces.

  Changed in version 2.1.0: Changed indent from an integer number of spaces to a string.

  If specified, separators should be an `(item_separator, dict_separator)` tuple. By default, `(', ', ': ')` are used. To get the most compact JSON representation, you should specify `(',', ':')` to eliminate whitespace.

  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`.

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

  If use_decimal is true (default: `False`) then `decimal.Decimal` will be natively serialized to JSON with full precision.

  Changed in version 2.1.0: use_decimal is new in 2.1.0.

  Note

  JSON is not a framed protocol so unlike `pickle` or `marshal` it does not make sense to serialize more than one JSON document without some container protocol to delimit them.

`simplejson.``dumps`(obj[, skipkeys[, ensure_ascii[, check_circular[, allow_nan[, cls[, indent[, separators[, encoding[, default[, use_decimal[, **kw]]]]]]]]]]])

  Serialize obj to a JSON formatted `str`.

  If ensure_ascii is false, then the return value will be a `unicode` instance. The other arguments have the same meaning as in `dump()`. Note that the default ensure_ascii setting has much better performance.

`simplejson.``load`(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, use_decimal[, **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 `unicode` object and passed to `loads()`. The default setting of `'utf-8'` is fastest and should be using whenever possible.

  If fp.read() returns `str` then decoded JSON strings that contain only ASCII characters may be parsed as `str` for performance and memory reasons. If your code expects only `unicode` the appropriate solution is to wrap fp with a reader as demonstrated above.

  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 decode 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 2.1.0: 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.

  If use_decimal is true (default: `False`) then parse_float is set to `decimal.Decimal`. This is a convenience for parity with the `dump()` parameter.

  Changed in version 2.1.0: use_decimal is new in 2.1.0.

  To use a custom `JSONDecoder` subclass, specify it with the `cls` kwarg. Additional keyword arguments will be passed to the constructor of the class.

  > Note

  > `load()` will read the rest of the file-like object as a string and then call `loads()`. It does not stop at the end of the first valid JSON document it finds and it will raise an error if there is anything other than whitespace after the document. Except for files containing only one JSON document, it is recommended to use `loads()`.

`simplejson.``loads`(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, use_decimal[, **kw]]]]]]]]])

  Deserialize s (a `str` or `unicode` instance containing a JSON document) to a Python object.

  If s is a `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` first.

  If s is a `str` then decoded JSON strings that contain only ASCII characters may be parsed as `str` for performance and memory reasons. If your code expects only `unicode` the appropriate solution is decode s to `unicode` prior to calling loads.

  The other arguments have the same meaning as in `load()`.

## Encoders and decoders

class `simplejson.``JSONDecoder`([encoding[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, 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 `str` objects decoded by this instance (`'utf-8'` by default). It has no effect when decoding `unicode` objects.

  Note that currently only encodings that are a superset of ASCII work, strings of other encodings should be passed in as `unicode`.

  object_hook is an optional function that 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 is an optional function that will be called with the result of any object literal decode 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 2.1.0: 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.

  strict controls the parser’s behavior when it encounters an invalid control character in a string. The default setting of `True` means that unescaped control characters are parse errors, if `False` then control characters will be allowed in strings.

  `decode`(s)

    Return the Python representation of s (a `str` or `unicode` instance containing a JSON document)

    If s is a `str` then decoded JSON strings that contain only ASCII characters may be parsed as `str` for performance and memory reasons. If your code expects only `unicode` the appropriate solution is decode s to `unicode` prior to calling decode.

  `raw_decode`(s)

    Decode a JSON document from s (a `str` or `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 `simplejson.``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 `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, 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 `str` objects with all incoming unicode characters escaped. If ensure_ascii is false, the output will be a unicode object.

  If check_circular is false (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 (not 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 string, then JSON array elements and object members will be pretty-printed with a newline followed by that string repeated for each level of nesting. `None` (the default) selects the most compact representation without any newlines. For backwards compatibility with versions of simplejson earlier than 2.1.0, an integer is also accepted and is converted to a string with that many spaces.

  Changed in version 2.1.0: Changed indent from an integer number of spaces to a string.

  If specified, separators should be an `(item_separator, key_separator)` tuple. By default, `(', ', ': ')` are used. To get the most compact JSON representation, you should specify `(',', ':')` to eliminate whitespace.

  If specified, default should be 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`.

  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'`.

  `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)
           return JSONEncoder.default(self, o)

  `encode`(o)

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

        >>> import simplejson as json
        >>> 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 JSONEncoder().iterencode(bigobject):
            mysocket.write(chunk)

    Note that `encode()` has much better performance than `iterencode()`.

class `simplejson.``JSONEncoderForHTML`([skipkeys[, ensure_ascii[, check_circular[, allow_nan[, sort_keys[, indent[, separators[, encoding[, default]]]]]]]]])

  Subclass of `JSONEncoder` that escapes &, <, and > for embedding in HTML.

  Changed in version 2.1.0: New in 2.1.0

### Navigation

- index
- simplejson v2.1.1 documentation »