A Python implementation of the JSON5 data format.

Clone this repo:
  1. 2154e31 Bump to version v0.9.13. by Dirk Pranke · 11 months ago main v0.9.14
  2. ff2a072 Fix GitHub issue #63 - Handle `+Infinity` properly. by Dirk Pranke · 11 months ago
  3. 25ca192 Bump version to v0.9.13. by Dirk Pranke · 1 year, 1 month ago v0.9.13
  4. e47b861 Remove reference to additional_target_cpus by Sylvain Defresne · 1 year, 1 month ago
  5. 11e387d Bump to version 0.9.12. by Dirk Pranke · 1 year, 4 months ago v0.9.12


A Python implementation of the JSON5 data format.

JSON5 extends the JSON data interchange format to make it slightly more usable as a configuration language:

  • JavaScript-style comments (both single and multi-line) are legal.

  • Object keys may be unquoted if they are legal ECMAScript identifiers

  • Objects and arrays may end with trailing commas.

  • Strings can be single-quoted, and multi-line string literals are allowed.

There are a few other more minor extensions to JSON; see the above page for the full details.

This project implements a reader and writer implementation for Python; where possible, it mirrors the standard Python JSON API package for ease of use.

There is one notable difference from the JSON api: the load() and loads() methods support optionally checking for (and rejecting) duplicate object keys; pass allow_duplicate_keys=False to do so (duplicates are allowed by default).

This is an early release. It has been reasonably well-tested, but it is SLOW. It can be 1000-6000x slower than the C-optimized JSON module, and is 200x slower (or more) than the pure Python JSON module.

Please Note: This library only handles JSON5 documents, it does not allow you to read arbitrary JavaScript. For example, bare integers can be legal object keys in JavaScript, but they aren't in JSON5.

Known issues

  • Did I mention that it is SLOW?

  • The implementation follows Python3's json implementation where possible. This means that the encoding method to dump() is ignored, and unicode strings are always returned.

  • The cls keyword argument that json.load()/json.loads() accepts to specify a custom subclass of JSONDecoder is not and will not be supported, because this implementation uses a completely different approach to parsing strings and doesn't have anything like the JSONDecoder class.

  • The cls keyword argument that json.dump()/json.dumps() accepts is also not supported, for consistency with json5.load(). The default keyword is supported, though, and might be able to serve as a workaround.

Running the tests

To run the tests, setup a venv and install the required dependencies with pip install -e '.[dev]', then run the tests with python setup.py test.

Version History / Release Notes

  • v0.9.14 (2023-05-14)

  • v0.9.13 (2023-03-16)

    • GitHub PR #64 Remove a field from one of the JSON benchmark files to reduce confusion in Chromium.
    • No code changes.
  • v0.9.12 (2023-01-02)

    • Fix GitHub Actions config file to no longer test against Python 3.6 or 3.7. For now we will only test against an “oldest” release (3.8 in this case) and a “current” release (3.11 in this case).
  • v0.9.11 (2023-01-02)

    • GitHub issue #60 Fixed minor Python2 compatibility issue by referring to float("inf") instead of math.inf.
  • v0.9.10 (2022-08-18)

    • GitHub issue #58 Updated the //README.md to be clear that parsing arbitrary JS code may not work.
    • Otherwise, no code changes.
  • v0.9.9 (2022-08-01)

    • GitHub issue #57 Fixed serialization for objects that subclass int or float: Previously we would use the objects str implementation, but that might result in an illegal JSON5 value if the object had customized str to return something illegal. Instead, we follow the lead of the JSON module and call int.__repr__ or float.__repr__ directly.
    • While I was at it, I added tests for dumps(-inf) and dumps(nan) when those were supposed to be disallowed by allow_nan=False.
  • v0.9.8 (2022-05-08)

    • GitHub issue #47 Fixed error reporting in some cases due to how parsing was handling nested rules in the grammar - previously the reported location for the error could be far away from the point where it actually happened.
  • v0.9.7 (2022-05-06)

    • GitHub issue #52 Fixed behavior of default fn in dump and dumps. Previously we didn‘t require the function to return a string, and so we could end up returning something that wasn’t actually valid. This change now matches the behavior in the json module. Note: This is a potentially breaking change.
  • v0.9.6 (2021-06-21)

    • Bump development status classifier to 5 - Production/Stable, which the library feels like it is at this point. If I do end up significantly reworking things to speed it up and/or to add round-trip editing, that‘ll likely be a 2.0. If this version has no reported issues, I’ll likely promote it to 1.0.
    • Also bump the tested Python versions to 2.7, 3.8 and 3.9, though earlier Python3 versions will likely continue to work as well.
    • GitHub issue #46 Fix incorrect serialization of custom subtypes
    • Make it possible to run the tests if hypothesis isn't installed.
  • v0.9.5 (2020-05-26)

    • Miscellaneous non-source cleanups in the repo, including setting up GitHub Actions for a CI system. No changes to the library from v0.9.4, other than updating the version.
  • v0.9.4 (2020-03-26)

  • v0.9.3 (2020-03-17)

    • GitHub pull #35 Fix from pastelmind@ for dump() not passing the right args to dumps().
    • Fix from p.skouzos@novafutur.com to remove the tests directory from the setup call, making the package a bit smaller.
  • v0.9.2 (2020-03-02)

  • v0.9.1 (2020-02-09)

    • GitHub issue #33: Fix stray trailing comma when dumping an object with an invalid key.
  • v0.9.0 (2020-01-30)

    • GitHub issue #29: Fix an issue where objects keys that started with a reserved word were incorrectly quoted.
    • GitHub issue #30: Fix an issue where dumps() incorrectly thought a data structure was cyclic in some cases.
    • GitHub issue #32: Allow for non-string keys in dicts passed to dump()/dumps(). Add an allow_duplicate_keys=False to prevent possible ill-formed JSON that might result.
  • v0.8.5 (2019-07-04)

    • GitHub issue #25: Add LICENSE and README.md to the dist.
    • GitHub issue #26: Fix printing of empty arrays and objects with indentation, fix misreporting of the position on parse failures in some cases.
  • v0.8.4 (2019-06-11)

    • Updated the version history, too.
  • v0.8.3 (2019-06-11)

    • Tweaked the README, bumped the version, forgot to update the version history :).
  • v0.8.2 (2019-06-11)

    • Actually bump the version properly, to 0.8.2.
  • v0.8.1 (2019-06-11)

    • Fix bug in setup.py that messed up the description. Unfortunately, I forgot to bump the version for this, so this also identifies as 0.8.0.
  • v0.8.0 (2019-06-11)

    • Add allow_duplicate_keys=True as a default argument to json5.load()/json5.loads(). If you set the key to False, duplicate keys in a single dict will be rejected. The default is set to True for compatibility with json.load(), earlier versions of json5, and because it's simply not clear if people would want duplicate checking enabled by default.
  • v0.7 (2019-03-31)

    • Changes dump()/dumps() to not quote object keys by default if they are legal identifiers. Passing quote_keys=True will turn that off and always quote object keys.
    • Changes dump()/dumps() to insert trailing commas after the last item in an array or an object if the object is printed across multiple lines (i.e., if indent is not None). Passing trailing_commas=False will turn that off.
    • The json5.tool command line tool now supports the --indent, --[no-]quote-keys, and --[no-]trailing-commas flags to allow for more control over the output, in addition to the existing --as-json flag.
    • The json5.tool command line tool no longer supports reading from multiple files, you can now only read from a single file or from standard input.
    • The implementation no longer relies on the standard json module for anything. The output should still match the json module (except as noted above) and discrepancies should be reported as bugs.
  • v0.6.2 (2019-03-08)

  • v0.6.1 (2018-05-22)

    • Cleaned up a couple minor nits in the package.
  • v0.6.0 (2017-11-28)

    • First implementation that attempted to implement 100% of the spec.
  • v0.5.0 (2017-09-04)

    • First implementation that supported the full set of kwargs that the json module supports.