Convert JSON to python dataclass through stdin or file argument.

json2dataclass.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""Convert JSON to python dataclass."""
import argparse
import json
import select
from string import Template
import sys
from typing import Any, Tuple

TEMPLATE = Template(
    '''
$imports

# Setting init to false will ignore keys that are not in the dataclass, and
# pull them in via the constructor we define below.
@dataclass(init=False)
class $class_name:
    def __init__(self, **kwargs) -> None:
        """$class_name DataClass."""
        self.__dict__.update(kwargs)
    # strip out Optional parameter for elements that are required exist
$data
'''.strip()
)


def get_type_string(value: Any) -> Tuple[str, Any, bool]:
    """Get type string."""
    if isinstance(value, str):
        return "str", "''", False
    elif isinstance(value, int):
        return "int", 'None', False
    elif isinstance(value, float):
        return "float", 'None', False
    elif isinstance(value, bool):
        return "bool", 'None', False
    elif isinstance(value, list):
        return "List", '[]', True
    elif isinstance(value, dict):
        return "Dict", 'field(default_factory=dict)', True
    else:
        return "Any", None, True


def run(args):
    """Run."""
    print(args)


def main():
    """Run main function."""
    parser = argparse.ArgumentParser(
        formatter_class=argparse.RawDescriptionHelpFormatter,
        description=__doc__,
    )
    parser.add_argument(
        "-f",
        "--file",
        help="JSON file",
        type=str,
        default=None,
    )
    args = parser.parse_args()
    # args = parser.parse_args("-f ./test.txt".split())

    if not args.file:
        if select.select([sys.stdin], [], [], 0.0)[0]:
            content = sys.stdin.read()
        else:
            sys.stderr.write("No input file or stdin detected\n")
            parser.print_help()
            sys.exit(1)
    else:
        with open(args.file, "r") as f:
            content = f.read()
    data = json.loads(content)
    build_str = ["   "]
    imports = [
        "from dataclasses import dataclass",
        "from typing import Optional",
    ]
    # from typing import List
    for key, value in data.items():
        type_str, def_val, is_type = get_type_string(value)
        if is_type:
            imports.append("from typing import {}".format(type_str))
        build_str.append(f"    {key}: Optional[{type_str}] = {def_val}")
    build_str = "\n".join(build_str)
    print(
        TEMPLATE.substitute(
            class_name="DataClass",
            imports="\n".join(imports),
            data=build_str,
        )
    )


if __name__ == "__main__":
    main()