Parser and pretty-printer for JSON and JSON-ish data, on the command line or as a Python library.

Synopsis

Suppose you have a JavaScript object literal:

$ cat input.js
setConfig({editable: true, latlng: new LatLng(48.1434, 17.1082), last_modified: new Date(1995, 11, 17)})

or a Python repr expression:

$ cat input.py
{"_id": 73, "occur": OrderedDict([("doc1", 10), ("doc2", 1)]), "match": <_sre.SRE_Match object at 0x7f2b9eaa5f80>}

or a MongoDB document:

$ cat input.mongo
{"id": ObjectId("507f191e810c19729de860ea"), "last_modified": ISODate("2020-05-20T00:00:00Z")}

You can use the canif library to load up that data as Plain Old Data Structures:

>>> with open('input.js', 'rt', encoding='UTF-8') as file_in:
...    canif.load(file_in)
{'$$setConfig': [{'editable': True, 'latlng': {'$$new LatLng': [48.1434, 17.1082]}, 'last_modified': {'$$new Date': [1995, 11, 17]}}]}

>>> with open('input.py', 'rt', encoding='UTF-8') as file_in:
...    canif.load(file_in)
{'_id': 73, 'occur': {'$$OrderedDict': [[('doc1', 10), ('doc2', 1)]]}, 'match': '$repr<_sre.SRE_Match object at 0x7f2b9eaa5f80>'}

>>> with open('input.mongo', 'rt', encoding='UTF-8') as file_in:
...    canif.load(file_in)
{'id': {'$oid': ['507f191e810c19729de860ea']}, 'last_modified': {'$$ISODate': ['2020-05-20T00:00:00Z']}}

Think of it as a version of json.loads that accepts a wider syntax.

This can be useful when writing Web scrapers, as it allows you to parse JavaScript data structures without having to use a JavaScript interpreter or a full-blown syntax parser.

Command line usage

You can also use the canif command-line tool to pretty-print JSON-ish data:

$ canif < input.js
setConfig(
    {
        editable: true,
        latlng: new LatLng(
            48.1434,
            17.1082,
        ),
        last_modified: new Date(
            1995,
            11,
            17,
        ),
    },
)

$ canif < input.py
{
    "_id": 73,
    "occur": OrderedDict(
        [
            (
                "doc1",
                10,
            ),
            (
                "doc2",
                1,
            ),
        ],
    ),
    "match": <_sre.SRE_Match object at 0x7f2b9eaa5f80>,
}

$ canif < input.mongo
{
    "id": ObjectId(
        "507f191e810c19729de860ea",
    ),
    "last_modified": ISODate(
        "2020-05-20T00:00:00Z",
    ),
}

There's an option to convert the data to proper JSON:

$ canif -j < input.js
{
    "$$setConfig": [
        {
            "editable": true,
            "latlng": {
                "$$new LatLng": [
                    48.1434,
                    17.1082
                ]
            },
            "last_modified": {
                "$$new Date": [
                    1995,
                    11,
                    17
                ]
            }
        }
    ]
}

The program pretty-prints the data as it loads it, so it should be able to handle very large files.

Use --help for a quick rundown of available options:

$ canif --help
usage: canif [-h] [-i N | -f] [-j] [-T] [--single-document]
             [--ensure-ascii] [-I ENCODING] [-O ENCODING]

Pretty-print JSON and JSON-ish data

optional arguments:
  -h, --help            show this help message and exit
  -i N, --indent N      Indent each level by N spaces (0 means flat,
                        single-line output)
  -f, --flatten         Flatten output (equivalent to -i 0)
  -j, --json-output     Convert data to valid JSON if it wasn't
                        already (e.g. None becomes null)
  -T, --no-trailing-commas
                        Don't insert trailing commas after the last
                        item in a sequence. This is implied by
                        --json-output.
  --single-document     Check that the input consists of a single
                        document, rather that the default of
                        accepting a stream of documents
  --ensure-ascii        Ensure JSON output is ASCII by using \uXXXX
                        sequences in place of non-ASCII characters
  -I ENCODING, --input-encoding ENCODING
                        Character set used for decoding the input
                        (default: UTF-8)
  -O ENCODING, --output-encoding ENCODING
                        Character set used for encoding the output
                        (default: UTF-8)

Emacs bindings

If you happen to use Emacs' shell-mode, this can be very useful to format the logs or output of any Python program.

See canif.el for a simple function that you can bind to a keystroke and that will pretty-print the data structure at point.

Supported formats

Canif is for "JSON and JSON-ish" data. It can parse:

• plain JSON
• JavaScript object literals, including:
  • unquoted keys
  • trailing commas
  • // comments
  • empty array slots (e.g. [1,,,4])
• printed Python data structures, including
  • sets: {42}
  • tuples: ("one", "two", "three")
  • <repr> representations
• MongoDB BSON

The parsed data can be pretty-printed in a couple formats:

• verbatim (i.e. only whitespace and commas are modified)
• strict JSON

There are options to control the output, e.g. indent depth, trailing commas, etc.