Simple python rison encoder

rison.py

""" Simple RISON encoder. """
import re


def encode(obj) -> str:
    """ Encode an object to a RISON string. """

    # Objects
    if isinstance(obj, dict):
        return "({})".format(
            ",".join(
                "{}:{}".format(encode(key), encode(value))
                for key, value in obj.items()
            )
        )

    # Lists
    if isinstance(obj, list):
        return "!({})".format(",".join(encode(i) for i in obj))

    # Strings
    if isinstance(obj, str):
        if not obj:
            return "''"

        if re.match(r"^[^-0123456789!:(),*@$][^!:(),*@$]*$", obj):
            return obj

        obj = re.sub(
            r"(['!])",
            lambda match: (
                lambda char: '!' + char if char in "'!'" else char
            )(match.group(1)),
            obj
        )
        return "'%s'" % obj

    # Literals
    if obj is True:
        return '!t'
    if obj is False:
        return '!f'
    if obj is None:
        return '!n'

    # Numerics
    return str(obj)