Convert JSON to YAML in Python without any dependency.

jaml.py

"""
Convert JSON to colorful YAML.

Example: 
  $ alias jaml="python .../jaml.py"
  $ curl https://api.thecatapi.com/v1/images/search -s | jaml

License: MIT
"""


def dump(data, iter=False, color=False, indent=2):
    indent = ' ' * indent

    def clr(code, value):
        if not color:
            return value
        return f'\033[{code}m{value}\033[0m'

    def _dump(value):
        if value is None:
            yield clr('3;31', 'null')

        elif isinstance(value, bool):
            yield clr('3;31', str(value).lower())

        elif isinstance(value, (int, float)):
            yield clr(34, str(value))

        elif isinstance(value, str):
            if '\n' in value:
                yield clr(3, '|')
                for line in value.splitlines():
                    yield clr(3, line)
            else:
                yield clr(3, value or "''")

        elif isinstance(value, list):
            if value:
                for item in value:
                    for n, line in enumerate(_dump(item)):
                        yield (indent if n else clr(36, '- ')) + line
            else:
                yield '[]'

        elif isinstance(value, dict):
            if value:
                for key, val in value.items():
                    key = clr(32, str(key) + ':')
                    if isinstance(val, (list, dict)) and val:
                        yield key
                        for line in _dump(val):
                            yield indent + line
                    else:
                        for n, line in enumerate(_dump(val)):
                            yield (indent if n else key + ' ') + line
            else:
                yield '{}'

        else:
            raise NotImplementedError(type(value))

    generator = _dump(value=data)
    if iter:
        return generator
    else:
        return '\n'.join(list(generator))


if __name__ == '__main__':
    import json
    import sys

    if not sys.stdin.isatty():
        text = sys.stdin.read()
        try:
            data = json.loads(text)
        except Exception:
            print(text)
        else:
            print(dump(data, color=True))

TODO:

•   Support multiline strings
•  Handle trailing whitespace in strings.
• Handle special characters in strings, e.g. yaml/yaml-test-suite#125.

Testing is done by converting JSON to YAML and back and comparing the result to the initial input:

import datetime
import json
import sys

import ruamel.yaml  # pip install ruamel.yaml
import yaml         # pip install PyYAML

import jaml


def default(x):
    if isinstance(x, datetime.datetime):
        return x.isoformat().replace('000+00:00', 'Z')
    return repr(x)


def test(text):
    data = json.loads(text)
    v1 = json.dumps(data, indent=2, default=default)
    print(jaml.dump(data, color=True))
    yml = jaml.dump(data)
    data = ruamel.yaml.YAML(typ='safe', pure=True).load(yml)  # YAML 1.2
    # data = yaml.safe_load(yml)  # YAML 1.1
    v2 = json.dumps(data, indent=2, default=default)
    if v1 != v2:
        print('v1:', v1)
        print('v2:', v2)
        print("DIFF", file=sys.stderr)
        exit(1)


if __name__ == '__main__':
    if not sys.stdin.isatty():
        test(sys.stdin.read())
        exit()

    1 and test('''
        {"a": {"b": {"c": {"d": 1}}}}
    ''')