isoformat

#!/usr/bin/env python3

import argparse
import datetime
import sys

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Format datetime as ISO 8601")
    parser.add_argument(
        "format", type=str, help="datetime format of input",
    )
    parser.add_argument(
        "offset",
        type=str,
        nargs="?",
        default="+0000",
        help="offset to include, default +0000",
    )
    parser.add_argument(
        "datetime", type=str, nargs="?", help="datetime to format",
    )

    args = parser.parse_args()

    if args.datetime is None:
        args.datetime = sys.stdin.read().strip()

    try:
        tz = datetime.datetime.strptime(args.offset, "%z").tzinfo
        dt = datetime.datetime.strptime(args.datetime, args.format).astimezone(tz=tz)
        print(dt.isoformat(timespec="milliseconds"))
    except Exception as e:
        print("error: {}".format(e), file=sys.stderr)
        sys.exit(1)