#!/usr/bin/env python3

import argparse
import json
import sys
from csv import DictReader
from typing import Any, Dict, List, Optional, TextIO


def csv2json(fp: TextIO, fields: Optional[List[str]]) -> None:
    reader = DictReader(fp, fieldnames=fields)

    for row in reader:
        json.dump(row, sys.stdout)
        print()


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument(
        'file', nargs='?', type=argparse.FileType('r'), default=sys.stdin
    )
    parser.add_argument('--field', dest='fields', action='append')
    args = parser.parse_args()

    csv2json(args.file, args.fields)