# json --- JSON encoder and decoder

> synopsis: Encode and decode the JSON format. Source code: Lib/json/init.py JSON (JavaScript Object Notation) < specified by 7159 (which obsoletes 4627) and by ECMA-404 < is a lightweight data interchange format inspired by JavaScript < object literal syntax (although it is not a strict subset of Jav

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-python-563545335993cf59c237>
- Knowledge kind: `reference`
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- Updated: `2026-08-16T09:32:14.535512+00:00`
- Tags: `reference-seed`, `python`, `library`, `json`, `encoder`, `decoder`

## Provenance

- Source: <https://github.com/python/cpython/blob/f10166035d602da5052e8a48f9d5c216c57b401d/Doc/library/json.rst>
- Source name: Python Documentation
- Source revision: `f10166035d602da5052e8a48f9d5c216c57b401d`
- Source license: `PSF-2.0`
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## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

synopsis: Encode and decode the JSON format.

Source code: Lib/json/init.py

JSON (JavaScript Object Notation) &lt; specified by 7159 (which obsoletes 4627) and by ECMA-404 &lt; is a lightweight data interchange format inspired by JavaScript &lt; object literal syntax (although it is not a strict subset of JavaScript [#rfc-errata]_ ).

The term "object" in the context of JSON processing in Python can be ambiguous. All values in Python are objects. In JSON, an object refers to any data wrapped in curly braces, similar to a Python dictionary.

Be cautious when parsing JSON data from untrusted sources. A malicious JSON string may cause the decoder to consume considerable CPU and memory resources. Limiting the size of data to be parsed is recommended.

This module exposes an API familiar to users of the standard library marshal and pickle modules.

Encoding basic Python object hierarchies

Customizing JSON object encoding

&gt;&gt;&gt; import json &gt;&gt;&gt; def custom_json(obj): ... if isinstance(obj, complex): ... return {'complex': True, 'real': obj.real, 'imag': obj.imag} ... raise TypeError(f'Cannot serialize object of {type(obj)}') ... &gt;&gt;&gt; json.dumps(1 + 2j, default=custom_json) '{"complex": true, "real": 1.0, "imag": 2.0}'

Customizing JSON object decoding

Using !json from the shell to validate and pretty-print

Bounded code example (external data; do not execute automatically):
```shell-session
$ echo '{"json":"obj"}' | python -m json
{
"json": "obj"
}
$ echo '{1.2:3.4}' | python -m json
Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
```

See json-commandline for detailed documentation.

JSON is a subset of YAML &lt; 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.

This module's encoders and decoders preserve input and output order by default. Order is only lost if the underlying containers are unordered.

Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.