Python: json module

Examples

import json

data = {'name': 'Joe Smith', 'info': {'age': 20}}

json_str = json.dumps(data)  # Python object to str
json_str = json.dumps(data, indent=2)  # pretty print
json_str = json.dumps(data, skipkeys=True)  # don't throw TypeError for keys that are not basic types

str = '{"name": "Joe Smith", "info": {"age": 20}}'

data = json.loads(str)  # str to Python object

with open("data.json", "w") as f:
    json.dump(data, f)  # use "dump" without "s" to write to file-like object "f"

with open("data.json", "r") as f:
    data = json.load(f)  # use "load" without "s" to read from file-like object "f"
$ python3
>>> import json

>>> dir(json)
['JSONDecodeError', 'JSONDecoder', 'JSONEncoder', '__all__', '__author__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__', '__version__', '_default_decoder', '_default_encoder', 'codecs', 'decoder', 'detect_encoding', 'dump', 'dumps', 'encoder', 'load', 'loads', 'scanner']

>>> help(json)

Help on package json:

NAME
    json

MODULE REFERENCE
    https://docs.python.org/3.6/library/json

    The following documentation is automatically generated from the Python
    source files.  It may be incomplete, incorrect or include features that
    are considered implementation detail and may vary between Python
    implementations.  When in doubt, consult the module reference at the
    location listed above.

DESCRIPTION
    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(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 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)
    class JSONDecoder(builtins.object)
     |  Simple JSON <http://json.org> 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.
  class JSONEncoder(builtins.object)
     |  Extensible JSON <http://json.org> encoder for Python data structures.
     |
     |  Supports the following objects and types by default:
     |
     |  +-------------------+---------------+
     |  | Python            | JSON          |
     |  +===================+===============+
     |  | dict              | object        |
     |  +-------------------+---------------+
     |  | list, tuple       | array         |
     |  +-------------------+---------------+
     |  | str               | string        |
     |  +-------------------+---------------+
     |  | int, 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``).
     |
>>> help(json.dumps)

Help on function dumps in module 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``.

    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.
>>> help(json.dump)

Help on function dump in module 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).
...
>>> help(json.loads)

Help on function loads in module 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``, ``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.
>>> help(json.load)

Help on function load in module 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.

Also See

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